From Wikipedia: The System Reference Document (SRD) was published in 2000 by Wizards of the Coast and is based on Dungeons & Dragons (3rd Edition); it was revised following the release of Dungeons & Dragons (3.5 Edition), in 2003. The SRD allows for third-party publishers to freely produce material compatible with D&D. It also forms the basis for independent role-playing games from other publishers, such as Mutants & Masterminds and Pathfinder Roleplaying Game (1st Edition), among others. User summary: The SRD (3.0) originally was offered as a series of eight topically organized RTF files that collectively constituted the entire document. The Revised SRD (3.5) originally was offered as a series of eighty-six topically organized RTF files that collectively constituted the entire document. The original download page also included the option to download seven topically grouped ZIP archives or a single ZIP archive - these archives contained the same content. Both the original and the revised SRD often were accompanied by supplemental files, such as the OGL, licensing materials, and introductory guides. These materials were not considered part of the SRD. Numerous online - usually HTML - conversions have also been produced by, de facto licensed, 3rd parties.