Free software licence
Encyclopedia
A free software licence is a software licence which grants recipients rights to modify and redistribute the software, which would otherwise be prohibited by copyright
law. A free software licence grants, to the recipients, freedoms in the form of permissions to modify or distribute copyrighted work. This freedom is not binary and licences can allow the user more or less freedom.
produced individual free software licences for each of its software packages. The first free licence in history, the GCC General Public License, was applied to the GNU Compiler Collection
and was initially published in 1987. The Original BSD license is also one of the first free software licences, dating to 1988. In 1989, version 1 of the GNU General Public License
(GPL) was published. Version 2 of the GPL, released in 1991, went on to become the most widely used free software licence. Starting in the mid-90s and until the mid-00s, a trend began where companies and new projects wrote their own licences, or adapting others' licences to insert their own name. This licence proliferation led to problems of complexity and licence compatibility. One free software licence, the GNU GPL version 2, has been brought to court, first in Germany and later in the USA. In the German case the judge did not explicitly discuss the validity of the GPL's clauses but accepted that the GPL had to be adhered to::If the GPL were not agreed upon by the parties, defendant would notwithstanding lack the necessary rights to copy, distribute, and make the software 'netfilter/iptables' publicly available.Because the defendant did not comply with the GPL, it had to cease use of the software. The US case (MySQL
vs Progress) was settled before a verdict was arrived at, but at an initial hearing, Judge Saris "saw no reason" that the GPL would not be enforceable.
, the group that maintains The Free Software Definition
, maintains a non-exhaustive list of free software licences. The list distinguishes between free software licences that are compatible or incompatible with the FSF licence of choice, the GNU General Public License
, which is a copyleft
licence. The list also contains licences which the FSF considers non-free for various reasons, but which are sometimes mistaken as being free.
(OSI), also maintains a list of approved licences. OSI and FSF agree on all widely used free software licences. OSI's list is different from FSF's list because the two organizations have reviewed different sets of licences. There are a few licences that OSI have approved that the FSF has not, and vice versa, but these are licences that are used by niche projects or none at all.
regarding the fine line between what restrictions can be applied and still be called "free".
During the 1990s, free software licences began including clauses, such as patent retaliation, in order to protect against software patent
litigation cases - a problem which had not previously existed. This new threat was one of the reasons for writing version 3 of the GNU GPL in 2006. In recent years, a term coined tivoization
describes a process where private modification of software under copyleft licenses are preventing to run by the use of hardware restrictions, which the Tivo
device is an example of. It is viewed by the FSF as a way to turn free software to effectively non-free, and is why they have chosen to prohibit it in GPLv3.
in the mid-1980s pioneered a concept known as copyleft
. Ensuing copyleft provisions stated that when modified versions of free software are distributed, they must be distributed under the same terms as the original software. This is sometimes referred to as "share and share alike" or "quid pro quo". This results in the new software being open source as well. This restriction is still usually called "Free Software".
Developers who use GPL code in their product must make the source code
available to anyone when they share or sell the object code
. In this case, the source code must also contain any changes the developers may have made. If GPL code is used but not shared or sold, the code is not required to be made available and any changes may remain private. This permits developers and organizations to use and modify GPL code for private purposes (i.e. when the code or the project is not sold or otherwise shared) without being required to make their changes available to the public.
Supporters of GPL claim that by mandating that derivative works remain under the GPL, it fosters the growth of free software and requires equal participation by all users. Opponents of GPL state that "no license can guarantee future software availability" and that the disadvantages of GPL outweigh its advantages. They also state that restricting distribution makes the licence less free.
may terminate a user's rights if said user embarks on litigation proceedings against them due to patent litigation. Patent retaliation emerged in response to proliferation and abuse of software patents.
and digital rights management (DRM)
, a practice FSF calls Tivoization
.
For example, if one licence says "modified versions must mention the developers in any advertising materials", and another licence says "modified versions cannot contain additional attribution requirements", then, if someone combined a software package which uses one licence with a software package which uses the other, it would be impossible to distribute the combination because these contradictory requirements cannot be simultaneously fulfilled. Thus, these two packages would be licence-incompatible.
For this reason, such licences are not considered free software by the standards of the FSF, OSI
, Debian
, or the BSD-based distributions.
The FSF's free software definition further states that development and distribution must not be restricted. Thus, commercial distribution of free software is acceptable and has become common.
-based operating systems have a different position on licensing. The main difference is the belief that the copyleft
licences, particularly the GNU General Public License
(GPL), are undesirably complicated and/or restrictive. The GPL requires any derivative work to also be released according to the GPL while the BSD licence does not. Essentially, the BSD licence's only requirement is to acknowledge the original authors, and poses no restrictions on how the source code
may be used. As a result, BSD code can be used in proprietary software
that only acknowledges the authors. For instance, the IP stack in Microsoft Windows NT 3.1 and Mac OS X
are derived from BSD-licensed software.
Supporters of the BSD licence argue that it is more free than the GPL because it grants the right to do anything with the source code, second only to software in the public domain
. This includes incorporating the BSD-licensed code into proprietary products. The approach has led to BSD code being used in common, widely used proprietary software. In response, GPL supporters claim that the freedom of others to make non-free software from free software is an unjust form of power rather than a necessary freedom. However, some developers might want to include GPLed software in their products and can't do it, simply because the GPL is incompatible with the licences of other software they include in their product, even if everything is open source.
Code licensed under a permissive free software license, such as the BSD licence, can be incorporated into copylefted (e.g. GPL'd) projects. Such code is thus "GPL-compatible". There is no need to secure the consent of the original authors. In contrast, code under the GPL cannot be relicensed under the BSD licence without securing the consent of all copyright holders. Thus the two licences are compatible, but the combination as a whole must be distributed under the terms of the GPL, not the permissive licence.
Existing free software BSDs tend to avoid including software licensed under the GPL in the core operating system, or the base system, except as a last resort when alternatives are non-existent or vastly less capable, such as with GCC
. (Indeed however, note that as of mid 2010 FreeBSD for example are moving from GCC
to the upcoming LLVM compiler, perhaps primarily for this reason.) The OpenBSD
project has acted to remove GPL-licensed tools in favor of BSD-licensed alternatives, some newly written and some adapted from older code.
project uses the criteria laid out in its Debian Free Software Guidelines
(DFSG). The only notable cases where Debian and Free Software Foundation disagree are over the Artistic License
and the GNU Free Documentation License
. Debian accepts the original Artistic License as being a free software licence, but FSF disagrees. This has very little impact however since the Artistic License is almost always used in a dual-license setup, along with the GNU General Public License
.
Regarding the GNU Free Documentation License, Debian decided to apply the DFSG to everything in their distribution, including documentation. The FSF argues that documentation is qualitatively different from software and is subject to different requirements. The end result of a long discussion and the eventual vote in Debian was that the works licensed under the GFDL are considered free as long as they do not contain unmodifiable sections (what the GFDL calls "Invariant Sections"). Most GNU documentation includes Invariant Sections.
Examples of licences which provoked debate include the 1.x series of the Apple Public Source License
, which were accepted by the Open Source Initiative but not by the Free Software Foundation or Debian, the RealNetworks Public Source License
, which was accepted by Open Source Initiative and Free Software Foundation but not by Debian, and in 2007, the Common Public Attribution License
, which was approved by Open Source Initiative
only.
Copyright
Copyright is a legal concept, enacted by most governments, giving the creator of an original work exclusive rights to it, usually for a limited time...
law. A free software licence grants, to the recipients, freedoms in the form of permissions to modify or distribute copyrighted work. This freedom is not binary and licences can allow the user more or less freedom.
History
In the mid-1980s, the GNU projectGNU Project
The GNU Project is a free software, mass collaboration project, announced on September 27, 1983, by Richard Stallman at MIT. It initiated GNU operating system development in January, 1984...
produced individual free software licences for each of its software packages. The first free licence in history, the GCC General Public License, was applied to the GNU Compiler Collection
GNU Compiler Collection
The GNU Compiler Collection is a compiler system produced by the GNU Project supporting various programming languages. GCC is a key component of the GNU toolchain...
and was initially published in 1987. The Original BSD license is also one of the first free software licences, dating to 1988. In 1989, version 1 of the GNU General Public License
GNU General Public License
The GNU General Public License is the most widely used free software license, originally written by Richard Stallman for the GNU Project....
(GPL) was published. Version 2 of the GPL, released in 1991, went on to become the most widely used free software licence. Starting in the mid-90s and until the mid-00s, a trend began where companies and new projects wrote their own licences, or adapting others' licences to insert their own name. This licence proliferation led to problems of complexity and licence compatibility. One free software licence, the GNU GPL version 2, has been brought to court, first in Germany and later in the USA. In the German case the judge did not explicitly discuss the validity of the GPL's clauses but accepted that the GPL had to be adhered to::If the GPL were not agreed upon by the parties, defendant would notwithstanding lack the necessary rights to copy, distribute, and make the software 'netfilter/iptables' publicly available.Because the defendant did not comply with the GPL, it had to cease use of the software. The US case (MySQL
MySQL
MySQL officially, but also commonly "My Sequel") is a relational database management system that runs as a server providing multi-user access to a number of databases. It is named after developer Michael Widenius' daughter, My...
vs Progress) was settled before a verdict was arrived at, but at an initial hearing, Judge Saris "saw no reason" that the GPL would not be enforceable.
FSF-approved "free software" licences
Free Software FoundationFree Software Foundation
The Free Software Foundation is a non-profit corporation founded by Richard Stallman on 4 October 1985 to support the free software movement, a copyleft-based movement which aims to promote the universal freedom to create, distribute and modify computer software...
, the group that maintains The Free Software Definition
The Free Software Definition
The Free Software Definition, written by Richard Stallman and published by Free Software Foundation , defines free software, as a matter of liberty, not price. The term "free" is used in the sense of "free speech," not of "free beer." The earliest known publication of the definition was in the...
, maintains a non-exhaustive list of free software licences. The list distinguishes between free software licences that are compatible or incompatible with the FSF licence of choice, the GNU General Public License
GNU General Public License
The GNU General Public License is the most widely used free software license, originally written by Richard Stallman for the GNU Project....
, which is a copyleft
Copyleft
Copyleft is a play on the word copyright to describe the practice of using copyright law to offer the right to distribute copies and modified versions of a work and requiring that the same rights be preserved in modified versions of the work...
licence. The list also contains licences which the FSF considers non-free for various reasons, but which are sometimes mistaken as being free.
OSI-approved "open source" licences
A group launched in 1998, Open Source InitiativeOpen Source Initiative
The Open Source Initiative is an organization dedicated to promoting open source software.The organization was founded in February 1998, by Bruce Perens and Eric S. Raymond, prompted by Netscape Communications Corporation publishing the source code for its flagship Netscape Communicator product...
(OSI), also maintains a list of approved licences. OSI and FSF agree on all widely used free software licences. OSI's list is different from FSF's list because the two organizations have reviewed different sets of licences. There are a few licences that OSI have approved that the FSF has not, and vice versa, but these are licences that are used by niche projects or none at all.
Restrictions
Certain licences restrict distribution in order to force derived projects to allow the freedom to use, study, modify, and redistribute the derived project. Some free software licences carry requirements and restrictions which apply to distributors. There exists an ongoing debate within the free software communityFree software community
The free-software community is an informal term that refers to the users and developers of free software as well as supporters of the free-software movement. The movement is sometimes referred to as the open-source software community or a subset thereof...
regarding the fine line between what restrictions can be applied and still be called "free".
During the 1990s, free software licences began including clauses, such as patent retaliation, in order to protect against software patent
Software patent
Software patent does not have a universally accepted definition. One definition suggested by the Foundation for a Free Information Infrastructure is that a software patent is a "patent on any performance of a computer realised by means of a computer program".In 2005, the European Patent Office...
litigation cases - a problem which had not previously existed. This new threat was one of the reasons for writing version 3 of the GNU GPL in 2006. In recent years, a term coined tivoization
Tivoization
Tivoization is a coined term to describe the creation of a system that incorporates software under the terms of a copyleft software license , but uses hardware restrictions to prevent users from running modified versions of the software on that hardware...
describes a process where private modification of software under copyleft licenses are preventing to run by the use of hardware restrictions, which the Tivo
TiVo
TiVo is a digital video recorder developed and marketed by TiVo, Inc. and introduced in 1999. TiVo provides an on-screen guide of scheduled broadcast programming television programs, whose features include "Season Pass" schedules which record every new episode of a series, and "WishList"...
device is an example of. It is viewed by the FSF as a way to turn free software to effectively non-free, and is why they have chosen to prohibit it in GPLv3.
Copyleft
The free software licences written by Richard StallmanRichard Stallman
Richard Matthew Stallman , often shortened to rms,"'Richard Stallman' is just my mundane name; you can call me 'rms'"|last= Stallman|first= Richard|date= N.D.|work=Richard Stallman's homepage...
in the mid-1980s pioneered a concept known as copyleft
Copyleft
Copyleft is a play on the word copyright to describe the practice of using copyright law to offer the right to distribute copies and modified versions of a work and requiring that the same rights be preserved in modified versions of the work...
. Ensuing copyleft provisions stated that when modified versions of free software are distributed, they must be distributed under the same terms as the original software. This is sometimes referred to as "share and share alike" or "quid pro quo". This results in the new software being open source as well. This restriction is still usually called "Free Software".
Developers who use GPL code in their product must make the source code
Source code
In computer science, source code is text written using the format and syntax of the programming language that it is being written in. Such a language is specially designed to facilitate the work of computer programmers, who specify the actions to be performed by a computer mostly by writing source...
available to anyone when they share or sell the object code
Object code
Object code, or sometimes object module, is what a computer compiler produces. In a general sense object code is a sequence of statements in a computer language, usually a machine code language....
. In this case, the source code must also contain any changes the developers may have made. If GPL code is used but not shared or sold, the code is not required to be made available and any changes may remain private. This permits developers and organizations to use and modify GPL code for private purposes (i.e. when the code or the project is not sold or otherwise shared) without being required to make their changes available to the public.
Supporters of GPL claim that by mandating that derivative works remain under the GPL, it fosters the growth of free software and requires equal participation by all users. Opponents of GPL state that "no license can guarantee future software availability" and that the disadvantages of GPL outweigh its advantages. They also state that restricting distribution makes the licence less free.
Patent retaliation
Most newly written free software licences since the late 1990s include some form of patent retaliation clauses. These measures stipulate that one's rights under the licence (such as to redistribution), may be terminated if one attempts to enforce patents relating to the licensed software, under certain circumstances. As an example, the Apple Public Source LicenseApple Public Source License
The Apple Public Source License is the open source and free software license under which Apple's Darwin operating system was released. A free software and open source license was voluntarily adopted to further involve the community from which much of Darwin originated.The first version of the Apple...
may terminate a user's rights if said user embarks on litigation proceedings against them due to patent litigation. Patent retaliation emerged in response to proliferation and abuse of software patents.
Hardware restrictions
Version 3 of the GNU GPL includes specific language prohibiting additional restrictions being enforced by hardware restrictionsHardware restrictions
Hardware restrictions refers to restrictions in any device that places technical restrictions on what content can run/play on said device or what users can do with certain content. Hardware restrictions can be used with software DRM and digital signatures...
and digital rights management (DRM)
Digital rights management
Digital rights management is a class of access control technologies that are used by hardware manufacturers, publishers, copyright holders and individuals with the intent to limit the use of digital content and devices after sale. DRM is any technology that inhibits uses of digital content that...
, a practice FSF calls Tivoization
Tivoization
Tivoization is a coined term to describe the creation of a system that incorporates software under the terms of a copyleft software license , but uses hardware restrictions to prevent users from running modified versions of the software on that hardware...
.
Attribution, disclaimers and notices
The majority of free software licences require that modified software not claim to be unmodified. Some licences also require that copyright holders be credited. One such example is version 2 of the GNU GPL, which requires that interactive programs that print warranty or licence information, may not have these notices removed from modified versions intended for distribution.Licence compatibility
Licences of software packages containing contradictory requirements, render it impossible to combine source code from such packages in order to create new software packages.For example, if one licence says "modified versions must mention the developers in any advertising materials", and another licence says "modified versions cannot contain additional attribution requirements", then, if someone combined a software package which uses one licence with a software package which uses the other, it would be impossible to distribute the combination because these contradictory requirements cannot be simultaneously fulfilled. Thus, these two packages would be licence-incompatible.
Licence proliferation
Licence proliferation compounds the problems of licence incompatibility. It likewise burdens software developers and distributors by increasing the amount of legal documents they must read. licence proliferation gained momentum during the late 1990s and increased into the early 2000s. By the year 2005, it was being identified as a problematic phenomenon and the gratuitous writing of new licences became more frowned upon.Purpose of use
Restrictions on private use of the software ("use restrictions") are generally unacceptable. Examples include prohibiting the software to be used for military purposes, for comparison or benchmarking, for ethically-questionable means, or in commercial organisations.For this reason, such licences are not considered free software by the standards of the FSF, OSI
Open Source Initiative
The Open Source Initiative is an organization dedicated to promoting open source software.The organization was founded in February 1998, by Bruce Perens and Eric S. Raymond, prompted by Netscape Communications Corporation publishing the source code for its flagship Netscape Communicator product...
, Debian
Debian
Debian is a computer operating system composed of software packages released as free and open source software primarily under the GNU General Public License along with other free software licenses. Debian GNU/Linux, which includes the GNU OS tools and Linux kernel, is a popular and influential...
, or the BSD-based distributions.
The FSF's free software definition further states that development and distribution must not be restricted. Thus, commercial distribution of free software is acceptable and has become common.
Permissive versus Copyleft opinions
Many users and developers of BSDBerkeley Software Distribution
Berkeley Software Distribution is a Unix operating system derivative developed and distributed by the Computer Systems Research Group of the University of California, Berkeley, from 1977 to 1995...
-based operating systems have a different position on licensing. The main difference is the belief that the copyleft
Copyleft
Copyleft is a play on the word copyright to describe the practice of using copyright law to offer the right to distribute copies and modified versions of a work and requiring that the same rights be preserved in modified versions of the work...
licences, particularly the GNU General Public License
GNU General Public License
The GNU General Public License is the most widely used free software license, originally written by Richard Stallman for the GNU Project....
(GPL), are undesirably complicated and/or restrictive. The GPL requires any derivative work to also be released according to the GPL while the BSD licence does not. Essentially, the BSD licence's only requirement is to acknowledge the original authors, and poses no restrictions on how the source code
Source code
In computer science, source code is text written using the format and syntax of the programming language that it is being written in. Such a language is specially designed to facilitate the work of computer programmers, who specify the actions to be performed by a computer mostly by writing source...
may be used. As a result, BSD code can be used in proprietary software
Proprietary software
Proprietary software is computer software licensed under exclusive legal right of the copyright holder. The licensee is given the right to use the software under certain conditions, while restricted from other uses, such as modification, further distribution, or reverse engineering.Complementary...
that only acknowledges the authors. For instance, the IP stack in Microsoft Windows NT 3.1 and Mac OS X
Mac OS X
Mac OS X is a series of Unix-based operating systems and graphical user interfaces developed, marketed, and sold by Apple Inc. Since 2002, has been included with all new Macintosh computer systems...
are derived from BSD-licensed software.
Supporters of the BSD licence argue that it is more free than the GPL because it grants the right to do anything with the source code, second only to software in the public domain
Public domain
Works are in the public domain if the intellectual property rights have expired, if the intellectual property rights are forfeited, or if they are not covered by intellectual property rights at all...
. This includes incorporating the BSD-licensed code into proprietary products. The approach has led to BSD code being used in common, widely used proprietary software. In response, GPL supporters claim that the freedom of others to make non-free software from free software is an unjust form of power rather than a necessary freedom. However, some developers might want to include GPLed software in their products and can't do it, simply because the GPL is incompatible with the licences of other software they include in their product, even if everything is open source.
Code licensed under a permissive free software license, such as the BSD licence, can be incorporated into copylefted (e.g. GPL'd) projects. Such code is thus "GPL-compatible". There is no need to secure the consent of the original authors. In contrast, code under the GPL cannot be relicensed under the BSD licence without securing the consent of all copyright holders. Thus the two licences are compatible, but the combination as a whole must be distributed under the terms of the GPL, not the permissive licence.
Existing free software BSDs tend to avoid including software licensed under the GPL in the core operating system, or the base system, except as a last resort when alternatives are non-existent or vastly less capable, such as with GCC
GNU Compiler Collection
The GNU Compiler Collection is a compiler system produced by the GNU Project supporting various programming languages. GCC is a key component of the GNU toolchain...
. (Indeed however, note that as of mid 2010 FreeBSD for example are moving from GCC
GNU Compiler Collection
The GNU Compiler Collection is a compiler system produced by the GNU Project supporting various programming languages. GCC is a key component of the GNU toolchain...
to the upcoming LLVM compiler, perhaps primarily for this reason.) The OpenBSD
OpenBSD
OpenBSD is a Unix-like computer operating system descended from Berkeley Software Distribution , a Unix derivative developed at the University of California, Berkeley. It was forked from NetBSD by project leader Theo de Raadt in late 1995...
project has acted to remove GPL-licensed tools in favor of BSD-licensed alternatives, some newly written and some adapted from older code.
Debian
The DebianDebian
Debian is a computer operating system composed of software packages released as free and open source software primarily under the GNU General Public License along with other free software licenses. Debian GNU/Linux, which includes the GNU OS tools and Linux kernel, is a popular and influential...
project uses the criteria laid out in its Debian Free Software Guidelines
Debian Free Software Guidelines
The Debian Free Software Guidelines is a set of guidelines that the Debian Project uses to determine whether a software license is a free software license, which in turn is used to determine whether a piece of software can be included in Debian...
(DFSG). The only notable cases where Debian and Free Software Foundation disagree are over the Artistic License
Artistic License
The Artistic License refers most commonly to the original Artistic License , a software license used for certain free and open source software packages, most notably the standard Perl implementation and most CPAN modules, which are dual-licensed under the Artistic License and the GNU General Public...
and the GNU Free Documentation License
GNU Free Documentation License
The GNU Free Documentation License is a copyleft license for free documentation, designed by the Free Software Foundation for the GNU Project. It is similar to the GNU General Public License, giving readers the rights to copy, redistribute, and modify a work and requires all copies and...
. Debian accepts the original Artistic License as being a free software licence, but FSF disagrees. This has very little impact however since the Artistic License is almost always used in a dual-license setup, along with the GNU General Public License
GNU General Public License
The GNU General Public License is the most widely used free software license, originally written by Richard Stallman for the GNU Project....
.
Regarding the GNU Free Documentation License, Debian decided to apply the DFSG to everything in their distribution, including documentation. The FSF argues that documentation is qualitatively different from software and is subject to different requirements. The end result of a long discussion and the eventual vote in Debian was that the works licensed under the GFDL are considered free as long as they do not contain unmodifiable sections (what the GFDL calls "Invariant Sections"). Most GNU documentation includes Invariant Sections.
Controversial borderline cases
The vast majority of free software uses undisputed free software licences; however, there have been many debates over whether or not certain other licences qualify for the definition.Examples of licences which provoked debate include the 1.x series of the Apple Public Source License
Apple Public Source License
The Apple Public Source License is the open source and free software license under which Apple's Darwin operating system was released. A free software and open source license was voluntarily adopted to further involve the community from which much of Darwin originated.The first version of the Apple...
, which were accepted by the Open Source Initiative but not by the Free Software Foundation or Debian, the RealNetworks Public Source License
RealNetworks Public Source License
The RealNetworks Public Source License is a software licence. It has been approved as a free software licence by both Free Software Foundation and Open Source Initiative , but it is incompatible with the GPL and the Debian Free Software Guidelines.The RPSL is used by the Helix project.-External...
, which was accepted by Open Source Initiative and Free Software Foundation but not by Debian, and in 2007, the Common Public Attribution License
Common Public Attribution License
The Common Public Attribution License is a free software license approved by the Open Source Initiative in 2007. Its purpose is to be a general license for software distributed over a network...
, which was approved by Open Source Initiative
Open Source Initiative
The Open Source Initiative is an organization dedicated to promoting open source software.The organization was founded in February 1998, by Bruce Perens and Eric S. Raymond, prompted by Netscape Communications Corporation publishing the source code for its flagship Netscape Communicator product...
only.
See also
- Comparison of free software licenses
- BSD licensesBSD licensesBSD licenses are a family of permissive free software licenses. The original license was used for the Berkeley Software Distribution , a Unix-like operating system after which it is named....
- CopyleftCopyleftCopyleft is a play on the word copyright to describe the practice of using copyright law to offer the right to distribute copies and modified versions of a work and requiring that the same rights be preserved in modified versions of the work...
- Free software movementFree software movementThe free software movement is a social and political movement with the goal of ensuring software users' four basic freedoms: the freedom to run their software, to study and change their software, and to redistribute copies with or without changes. The alternative terms "software libre", "open...
- GPL linking exceptionGPL linking exceptionA GPL linking exception modifies the GNU General Public License to create a new, modified license. Such modified licenses enable software projects which provide library code, to be "linked to" the programs that use them, without applying the full terms of the GPL to the using program...
- Permissive free software license
- Software license agreementSoftware license agreementA software license agreement is a contract between the "licensor" and purchaser of the right to use software. The license may define ways under which the copy can be used, in addition to the automatic rights of the buyer including the first sale doctrine and .Many form contracts are only contained...
External links
- The Free Software Definition (Free Software Foundation).
- The Free Software Foundation's list of free and non-free licenses
- Debian's license information page
- Open Source Initiative's list of licenses
- OpenBSD's "goals" page describes its view of free software
- Transcripts of license strategy discussions, mostly of Stallman and Moglen, during the drafting of GPLv3
- Understanding Open Source and Free Software Licensing, by Andrew M. St. Laurent
- Report on free software business models and licensing (58 pages)
- A comparison of free open source software licenses, by Jeremy Hollander
- A 45-page licensing primer by Software Freedom Law Center