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Multi-licensing is the practice of distributing software under two or more different sets of terms and conditions. This may mean multiple different licenses or sets of licenses. Prefixes may be used to indicate the number of licenses used, e.g. dual-licensed for software licensed under two different licenses.

When software is multi-licensed, recipients can choose which terms under which they want to use or distribute the software. The distributor may or may not apply a fee to either option. The two usual motivations for multi-licensing are license compatibility
License compatibility
License compatibility refers to the problem with licenses applied to works subject to copyright, particularly licenses of software packages, which can contain contradictory requirements, rendering it impossible to combine source code from such packages or content from such works in order to create...

 and market segregation based business models.

Business models

Multi-licensing is commonly done to support free software
Free software
Free software, software libre or libre software is software that can be used, studied, and modified without restriction, and which can be copied and redistributed in modified or unmodified form either without restriction, or with restrictions that only ensure that further recipients can also do...

 business models in a commercial environment. In this scenario, one option is a proprietary software license, which allows the possibility of creating proprietary applications
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...

 derived from it, while the other license 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...

 free software/open-source license
Open-source license
An open-source license is a copyright license for computer software that makes the source code available for everyone to use. This allows end users to review and modify the source code for their own customization and/or troubleshooting needs...

, thus requiring any derived work to be released under the same license. The copyright holder of the software then typically provides the free version of the software at little or no cost, and profits by selling proprietary licenses to commercial operations looking to incorporate the software into their own business. This model can be compared to shareware
Shareware
The term shareware is a proprietary software that is provided to users without payment on a trial basis and is often limited by any combination of functionality, availability, or convenience. Shareware is often offered as a download from an Internet website or as a compact disc included with a...

.

Since in most cases, only the copyright holder can change the licensing terms of a software, multi licensing is mostly used by companies that wholly own the software which they are licensing. Confusion may arise when a person outside the company creates additional source code, using the less restrictive license. Because the company with the official code is not the copyright holder of the additional code, they may not legally include this new work in their more restrictively licensed version. Companies may demand outside developers agree to a contributor license agreement, before accepting their work in the official codebase and source code repositories.

Multi licensing is used by the copyright holders of some free software
Free software
Free software, software libre or libre software is software that can be used, studied, and modified without restriction, and which can be copied and redistributed in modified or unmodified form either without restriction, or with restrictions that only ensure that further recipients can also do...

 packages advertising their willingness to distribute using both 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...

 free software license and a non-free software license. The latter license typically offers users the software as 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...

 or offers third parties the source code without copyleft provisions. Copyright holders are exercising the monopoly they're provided under copyright
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...

 in this scenario, but also use multi licensing to discriminate the rights and freedoms different recipients receive.

Such licensing allows the holder to offer customizations and early releases, generate other derivative works or grant rights to third parties to redistribute proprietary versions all while offering everyone a free version of the software. Sharing the package as copyleft free software can benefit the copyright holder by receiving contributions from users and hackers of the free software community
Free 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...

. These contributions can be the support of a dedicated user community, word of mouth
Word of mouth
Word of mouth, or viva voce, is the passing of information from person to person by oral communication. Storytelling is the oldest form of word-of-mouth communication where one person tells others of something, whether a real event or something made up. Oral tradition is cultural material and...

 marketing or modifications that are made available as stipulated by a copyleft license. However, a copyright holder's commitment to elude copyleft provisions and advertise proprietary redistributions risks losing confidence and support from free software users.

Examples include MySQL AB
MySQL AB
MySQL AB was a software company. MySQL AB is the creator of MySQL, a relational database management system, as well as related products such as MySQL Cluster...

's database, Asterisk
Asterisk (PBX)
Asterisk is a software implementation of a telephone private branch exchange ; it was created in 1999 by Mark Spencer of Digium. Like any PBX, it allows attached telephones to make calls to one another, and to connect to other telephone services including the public switched telephone network and...

, Oracle Corporation
Oracle Corporation
Oracle Corporation is an American multinational computer technology corporation that specializes in developing and marketing hardware systems and enterprise software products – particularly database management systems...

's Berkeley DB
Berkeley DB
Berkeley DB is a computer software library that provides a high-performance embedded database for key/value data. Berkeley DB is a programmatic software library written in C with API bindings for C++, PHP, Java, Perl, Python, Ruby, Tcl, Smalltalk, and most other programming languages...

, ZeroC
ZeroC
ZeroC, Inc. is a company based in Palm Beach Gardens, Florida, U.S., revolving around the development and licensing of the Internet Communications Engine, or ICE, an object middleware system considered an alternative to CORBA and SOAP...

's Ice
Internet Communications Engine
The Internet Communications Engine, or Ice, is an object-oriented middleware that provides object-oriented Remote Procedure Call, grid computing and Publish/subscribe functionality developed by ZeroC and dual-licensed under the GNU GPL and a proprietary license...

, and Qt Software's Qt
Qt (toolkit)
Qt is a cross-platform application framework that is widely used for developing application software with a graphical user interface , and also used for developing non-GUI programs such as command-line tools and consoles for servers...

 development toolkit.

License compatibility

A second use of multi-licensing with free software is for license compatibility, allowing code from differently licensed free software projects to be combined, or to provide users the preference to pick a license.

Examples include the source code of Mozilla Application Suite
Mozilla Application Suite
The Mozilla Application Suite is a cross-platform integrated Internet suite. Its development was initiated by Netscape Communications Corporation, before their acquisition by AOL. It is based on the source code of Netscape Communicator...

, Mozilla Thunderbird
Mozilla Thunderbird
Mozilla Thunderbird is a free, open source, cross-platform e-mail and news client developed by the Mozilla Foundation. The project strategy is modeled after Mozilla Firefox, a project aimed at creating a web browser...

 and Mozilla Firefox
Mozilla Firefox
Mozilla Firefox is a free and open source web browser descended from the Mozilla Application Suite and managed by Mozilla Corporation. , Firefox is the second most widely used browser, with approximately 25% of worldwide usage share of web browsers...

, which is tri-licensed under the Mozilla Public License
Mozilla Public License
The Mozilla Public License is a free and open source software license. Version 1.0 was developed by Mitchell Baker when she worked as a lawyer at Netscape Communications Corporation and version 1.1 at the Mozilla Foundation...

 (MPL), 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) or GNU Lesser General Public License
GNU Lesser General Public License
The GNU Lesser General Public License or LGPL is a free software license published by the Free Software Foundation . It was designed as a compromise between the strong-copyleft GNU General Public License or GPL and permissive licenses such as the BSD licenses and the MIT License...

 (LGPL); Perl
Perl
Perl is a high-level, general-purpose, interpreted, dynamic programming language. Perl was originally developed by Larry Wall in 1987 as a general-purpose Unix scripting language to make report processing easier. Since then, it has undergone many changes and revisions and become widely popular...

, which is dual-licensed under the GPL or 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 Ruby
Ruby (programming language)
Ruby is a dynamic, reflective, general-purpose object-oriented programming language that combines syntax inspired by Perl with Smalltalk-like features. Ruby originated in Japan during the mid-1990s and was first developed and designed by Yukihiro "Matz" Matsumoto...

, whose license
Ruby License
The Ruby License is the open-source license applied to the Ruby programming language and also available to be used in other projects.The Free Software Foundation comments:...

 contains explicit GPL dual licensing.

Market segregation in proprietary software

Multi licensing is also used by distributors of non-free software. Sometimes this is done to proprietary software to segregate a market. By splitting customers into multiple categories such as home users, professional users, and academic users, copyright holders can set different prices for each group. However, among proprietary software companies, it is more common to release a "home edition" and a "professional edition" of a given product, which differ by the software and software features included, not just the license.

See also

  • Business models for open source software
    Business models for open source software
    There are several different types of business models for making profit using open source software .- Introduction :Open source software can be sold and used commercially. It is a part of the software industry. The financial return on open source software can also come from selling services, such...

  • Commercial open source applications
    Commercial open source applications
    Open source software is widely used for private and non-commercial applications. In addition, many independent software vendors , value-added resellers , and hardware vendors use open source frameworks, modules, and libraries inside their proprietary, for-profit products and services...

  • Professional open-source
    Professional open-source
    Professional open-source is an open source software business model where an open source software vendor generates revenue from paid professional services, maintenance and support provided along with the software...


External links

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
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