Open Game License
 Open Game License
The Open Game License is an open license created by Wizards of the Coast to support its d20 line of role-playing games, in particular the third edition of Dungeons and Dragons. A license for a document is generally considered "open" if it allows for the redistribution and modification of the document without further permission from the original creator. This is a concept that was first introduced for the source code for software, and the GNU license is, perhaps, the most well-known example.
In addition to the OGL, Wizards of the Coast created a more restrictive d20 license. The d20 license is more restrictive than the OGL and requires explicit approval from Wizards of the Coast before publication of a product using that license.
The original justification for the open game license was to promote a more unified role-playing-game community and market. It is widely believed that it was extremely successful in this regard. It is also believed that this led to much of the continued success of Dungeons and Dragons 3.0 and 3.5.
Wizards of the Coast has released the fourth edition of Dungeons and Dragons under the Game System License, a license significantly different to the OGL.
 Versions of the OGL
One of the unusual strengths of the OGL is clause 9, which allows for any version of the license to be used for any document released under any version of the license. Thus, if a document is released under version 1.0b, anyone may choose to use the document as if it were released under version 1.0a.
Versions of the OGL:
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