Open Game License

The Open Game License (or OGL) is a public copyright license that may be used by tabletop role-playing game developers to grant permission to modify, copy, and redistribute some of the content designed for their games, notably game mechanics. However, they must share-alike copies and derivative works.

Language of the license
The OGL describes two forms of content:

Open Game Content (or OGC)



Product Identity (or PI)



Product Identity is content covered by normal copyright.

Using the OGL
By attaching this license game developers allow the use of their OGC and any additional content they may have indicated to be OGC. This use is perpetual, worldwide, royalty-free, and non-exclusive as long as the use is accompanied by a copy of the OGL with all the Copyrights updated to credit the contributors of all OGC that was used. All used OGC is to be indicated with a notice.

Licensees are prevented from distributing, copying, or modifying PI, and may not use the contributor's name for the purposes of marketing or advertising, unless permission is acquired through a separate license or agreement with the holders of the PI.

Finally, the OGL requires attribution be maintained by the copying of all copyright notices from OGC a licensee is copying, modifying or distributing. This requires that the license notice itself must be altered by adding all copyright notices to the Section 15 part of the license.

Background
It was published by Wizards of the Coast in 2000 to license their Dungeons & Dragons game as the System Reference Document, or SRD, in a move spearheaded by Ryan Dancey. It is commonly used with the d20 license to allow individuals, amateur and professional companies and groups to publish the SRD and derivative works under the d20 System trademark. In June 2008, Wizards of the Coast transitioned to a new, more restrictive royalty-free license called the Game System License (GSL), which is available for third-party developers to publish products compatible with Dungeons & Dragons 4th edition. The GSL is incompatible with the previous OGL, however the OGL is non-revokable, and remains in widespread use.

Those individuals, groups and publishing companies that license their works under the OGL and similar documents are sometimes collectively referred to as the "open gaming movement".