An invitation system is a method of joining an organization, such as a club or a website. In regular society, it refers to any system whereby new members are chosen; they cannot simply apply. In relation to websites and other technology-related organisations, the term refers to a more specific situation whereby invitations are sent, but there is never any approval needed from other members. Popular alternatives to this specific version are open registration and closed registration. Open registration is where any user can freely join. Closed registration involves an existing member recommending a new member and approval is sought amongst the existing members. The basis of the invitation system is that a member can grant approval to a new user without having to consult any other members.

Existing members may receive a set number of invitations (sometimes in the form of tokens) to allow others to join the service. Those invited to a website are typically sent either a specialized URL

Uniform Resource Locator

In computing, a uniform resource locator or universal resource locator is a specific character string that constitutes a reference to an Internet resource....

 or a single-use pass code.

Applications

Invitation systems for websites are usually temporary. They are typically used for services in private beta testing, in order to control the number of users on the service. In other cases, they can be used due to limited availability of server

Server (computing)

In the context of client-server architecture, a server is a computer program running to serve the requests of other programs, the "clients". Thus, the "server" performs some computational task on behalf of "clients"...

 resources. There are a growing number of sites which use invitation systems on a permanent basis to create exclusivity and to control quality of user-generated content. Rarely, they may be used on a permanent basis in order to aggregate social network

Social network

A social network is a social structure made up of individuals called "nodes", which are tied by one or more specific types of interdependency, such as friendship, kinship, common interest, financial exchange, dislike, sexual relationships, or relationships of beliefs, knowledge or prestige.Social...

 statistics (all users will ultimately have a traceable connection to all others). They are sometimes used to avoid abusive types or spammers

Spam (electronic)

Spam is the use of electronic messaging systems to send unsolicited bulk messages indiscriminately...

, by relying on mutual trust between all members.

Variations

Sometimes, a tiered invitation system may be in place, wherein those higher up the hierarchy will have the power to grant more invitations, whereas low-ranking members may receive few or even no invitation rights.

Examples

Some prominent services which were once invitation-based include blog

Blog

A blog is a type of website or part of a website supposed to be updated with new content from time to time. Blogs are usually maintained by an individual with regular entries of commentary, descriptions of events, or other material such as graphics or video. Entries are commonly displayed in...

-host LiveJournal

LiveJournal

LiveJournal is a virtual community where Internet users can keep a blog, journal or diary. LiveJournal is also the name of the free and open source server software that was designed to run the LiveJournal virtual community....

, social network Yahoo 360°, and podcast

Podcast

A podcast is a series of digital media files that are released episodically and often downloaded through web syndication...

 publisher Odeo

Odeo

Odeo was a directory and search destination website for RSS syndicated audio & video. It employed tools that enabled users to create, record, and share podcasts with a simple Adobe Flash-based interface....

. When Google

Google

Google Inc. is an American multinational public corporation invested in Internet search, cloud computing, and advertising technologies. Google hosts and develops a number of Internet-based services and products, and generates profit primarily from advertising through its AdWords program...

 releases new services, an invitation requirement has often been imposed for the first few months of the service's existence, including
e-mail

E-mail

Electronic mail, commonly known as email or e-mail, is a method of exchanging digital messages from an author to one or more recipients. Modern email operates across the Internet or other computer networks. Some early email systems required that the author and the recipient both be online at the...

 provider Gmail

Gmail

Gmail is a free, advertising-supported email service provided by Google. Users may access Gmail as secure webmail, as well via POP3 or IMAP protocols. Gmail was launched as an invitation-only beta release on April 1, 2004 and it became available to the general public on February 7, 2007, though...

, social networking service Orkut

Orkut

Orkut is a social networking website that is owned and operated by Google Inc. The service is designed to help users meet new and old friends and maintain existing relationships...

 and real-time collaboration site Google Wave

Google Wave

Apache Wave is a software framework for real-time collaborative editing online. Google Inc. originally developed it as Google Wave.It was announced at the Google I/O conference on May 27, 2009....

.

Many BitTorrent tracker

BitTorrent tracker

A BitTorrent tracker is a server that assists in the communication between peers using the BitTorrent protocol. It is also, in the absence of extensions to the original protocol, the only major critical point, as clients are required to communicate with the tracker to initiate downloads...

s, known as "private trackers", use an invitation system in order to maintain torrent quality, speeds, and safety. Demonoid

Demonoid

Demonoid is a website and BitTorrent tracker created by an anonymous Serb known only by the pseudonyms "Deimos" and "Zajson". The website indexes torrents uploaded by its members. Demonoid.com was ranked the 538th most popular website overall in December 2010, according to Alexa. Demonoid's torrent...

 and ImmortalSeed are examples of invitation-only trackers. Despite its invite-only status, Oink's Pink Palace

Oink's Pink Palace

Oink's Pink Palace was a prominent BitTorrent tracker which operated from 2004 to 2007. Following a two-year investigation by the International Federation of the Phonographic Industry , and the British Phonographic Industry , the site was shut down on 23 October 2007, by British and Dutch police...

was accessed by government authorities and forced to close in October 2007.