Those individuals, groups and publishing companies that license their works under the OGL are sometimes collectively referred to as the "open gaming movement".
In many respects, the OGL resembles any other open source license. This section deals primarily with the OGL's differences with standard, open source licenses.
The OGL describes two forms of content: Open Game Content (or OGC) and Product identity (or PI) - that is content covered by normal copyright, commonly referred to as "closed content". The OGL permits the inclusion of both OGC and PI within a single work. Publishers are required to "clearly indicate" those parts of a work that are OGC.
The OGL defines the concept of PI as:
PI must be clearly defined by the publisher and, by using the OGL, licensees are prevented from distributing, copying or modifying PI and claiming "compatibility or co-adaptability" with PI trademarks 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. Unlike other open source licenses, this requires that the license notice itself must be altered by adding all copyright notices to the Section 15 part of the license.
The GSL is incompatable with the previous OGL. The GSL directly prohibts material to be published both under the GSL (compatible with 4th Edition) as well as the OGL (compatible with 3rd Edition and Edition 3.5). Many publishers suggest this restriction represents a direct attack on the OGL which Wizards of the Coast is legally unable to revoke. The restriction has fostered some negative feelings within the adventure gaming community and has resulted in many publishers which previously supported the D20 game system to reject 4th Edition entirely, and continue to publish material for 3.5, under the OGL.