Open gaming
Open gaming is a movement within the tabletop role-playing game (RPG) industry with superficial similarities to the open source software movement. The key aspect is that copyright holders license their works under public copyright licenses that permit others to make copies or create derivative works of the game. A number of role-playing game publishers have joined the open gaming movement, largely as a result of the release of the original System Reference Document (SRD) by Wizards of the Coast, which consisted of the core rules of "Dungeons & Dragons" 3rd edition. Open gaming has also been popular  among small press role-playing game and supplement authors. History. The use of the term open gaming began with the publication of the original SRD and the simultaneous release of the Open Game License (OGL). However, role-playing games had been licensed under open and free content licenses before this. The Fudge Legal Notice. The Fudge role-playing game system was created in 1992 by Steffan O'Sullivan with extensive help from the rec.games.design community. The name stood for "Freeform Universal Donated Game Engine" until Steffan O'Sullivan changed 'donated' to 'DIY' in 1995. One reason why Fudge succeeded is that the  author released it under the "FUDGE Legal Notice", a license that removed most restrictions on non-commercial use. However the FUDGE Legal Notice (more commonly known as simply "the Fudge license") was never intended to cover any work other than its eponymous role-playing game. Derivative works which were to be distributed for a fee required written permission from Fudge's author, Steffan O'Sullivan. The details of the Fudge Legal Notice were modified and expanded from time to time as O'Sullivan updated his work, but the essential elements of the license remained unchanged. The 1993 FUDGE Legal Notice allowed reprinting  of the Fudge rules, including in otherwise commercial works, as long as certain conditions were met. The 1995 FUDGE Legal Notice permitted the creation of derivative works for personal use and for publication in periodicals. In March 2004, Grey Ghost Games acquired the copyright of Fudge, and on April 6, 2005, they released a version of Fudge under the Open Game License, making it open for commercial use. Dominion Rules and Circe. The phrase "opensource roleplaying" was used as early as 1999 by the Dominion Rules role-playing system, the license of which permitted supplementary material to be written for  its rules. Another "open" system was the Circe role-playing system, published by the WorldForge project under the GNU Free Documentation License. Open Game License. Despite Fudge and other games, the open gaming movement did not gain widespread recognition within the role-playing game industry until 2000, when Wizards of the Coast (WotC) published portions of the 3rd Edition of "Dungeons & Dragons" as the System Reference Document under the Open Game License. This move was driven by Ryan Dancey then Brand Manager for WotC, who drafted the Open Game License and first coined the term "open gaming" with respect to  role-playing games. Open Gaming Foundation. The Open Gaming Foundation (OGF) was founded by Ryan Dancey as an independent forum for discussion of open gaming among the members of the fledgling open gaming movement. The OGF consisted of a web site and a series of mailing lists, including the "OGF-L" list (for general discussion of open gaming licensing issues) and the "OGF-d20-L" list (for discussion of d20-specific issues). The most common criticism of the OGF was that it was primarily a venue for publicizing Wizards of the Coast. Ryan Dancey was an employee of WotC, and  discussion on the mailing lists tended to focus on d20 and the OGL (both owned by WotC) rather than on open gaming in general. The OGF maintained a definition of an "open game license" while it was active, with two criteria: “1. The license must allow game rules and materials that use game rules to be freely copied, modified and distributed. “2. The license must ensure that material distributed using the license cannot have those permissions restricted in the future.” The Foundation explicitly stated that the first condition excludes licences that ban commercial use. The second requirement is intended  to ensure that the rights granted by the licence are inalienable. Reaction. The OGL gained immediate popularity with commercial role-playing game publishers. However, the OGL was criticized (primarily by independent role-playing game developers) for being insufficiently "open", and for being controlled by the market leader Wizards of the Coast. In response to this, and in an attempt to shift support away from the OGL and toward more open licenses, several alternatives to the OGL were suggested and drafted. Similarly, the popularity of the OGL inspired others to create their own, specific open content licenses. Virtually none of these  gained acceptance beyond the works of the licenses' own authors, and many have since been abandoned. Adoption. The most common open gaming license in use by commercial role-playing game publishers is the OGL. There are many publishers currently producing material based on the first System Reference Document, and many which make their products available under the OGL but which use game systems not based on the SRD. Wizards of the Coast used the non-open Game System License for the 4th edition of "Dungeons & Dragons", but released a new System Reference Document in 2015 for the 5th edition licensed  under the OGL. Approved licences. The Open Gaming Foundation describes these licences as ‘Known Open Gaming Licenses’. Open games. The following games are under an Open Gaming Foundation-approved license or a free culture license. Retro-clone systems. A number of fans and publishers have used existing open game content to create rules systems which closely emulate older editions of games that are no longer supported, and released those rules systems under an open license. The term "retro-clone" was coined by Goblinoid Games, the publisher of Labyrinth Lord. Notable examples of retro-clone games are "OSRIC" (based on 1st  edition "Advanced Dungeons & Dragons"), "Labyrinth Lord" (based on "Basic Dungeons & Dragons"), and "Swords & Wizardry" (based on original "Dungeons & Dragons").