Open Game Systems

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This page collects games released under an open license. Generally speaking, if something is available under an open license it is free for use and re-use as long as the terms of its license are respected, without any explicit contact or negotiation between original author and licensee. Those vary from offering no restriction whatsoever to requiring that you credit the authors or that you also allow others to use your own derivative work freely.

The most common use of these licenses if for the original authors to inform other people interested in using their system that they are legally able to do so and even sell their own new work without having to pay anything to the original authors - however, even if those are intended as a gesture of good will and openness, failing to respect all of the terms from a license may leave you exposed to a lawsuit from the original creators.

Using an openly-licensed system for your own products (books, video games, card games...) means that you are able to rely on the work of others instead of having to design, write, playtest and balance your own. It also allows a product to become part of a larger community - which may draw players from that community to your product (since they're already familiar with the rules) or allow them to combine your product with others that use the same system.

Here is a brief description of each major license found on the list below. Note, however, that details vary from license to license - so if you're planning on doing anything more than using the systems below for personal play, you should get acquainted with the full text of the license:

  • Open Game License (OGL): the OGL allows for differentiation between Open Game Content (parts of the system that others can use freely) and Product Identity (parts that are not open for others to use). Some publishers also create a System Reference Document (SRD) that allows for use of copyrighted material under its own license.
  • Creative commons (CC): a family of permissive licenses that usually require only that you credit the original authors when using their work. Authors are free to choose from any of the CC licenses available - to read more about the differences between each, visit their official website.
  • GNU licenses (GPL and GFDL): designed for distribution of computer code and programs, this license allows you to use original work freely. However, if you are creating a modification of said work (for example, a set of alternative rules), you are required to make your own work available through the GPL license as well. If you are not modifying the original work, but only using it to create something entirely new (for example, a book with new characters and monsters to use) then you are not required to distribute it under the GPL. There are many versions of this license available, the most popular arguably being the GPLv2 - for more information about each version and related licenses see the official GNU website.

Open Game License

Note that the official d20 SRD for D&D 3e has been revoked. It has been replaced by Paizo's Pathfinder SRD, which is compatible with previous d20 material and still being used for publication of new products by the community by many companies.

d20 System-based


Other systems


Retro-clones are new games that are compatible with older games now out-of-print, allowing for the use of previous material without having to acquire a possibly rare and/or expensive copy of the original game or resorting to piracy. These are part of a larger movement known as the Old-School Renaissance (OSR).

OGL with trademark license

These games release their material as Open Game Content but also provide another, more restricted license to allow publishers to refer to Product Identity.

  • Mutant Future (OGL and Mutant Future Trademark License)
  • GORE (OGL and GORE License)
  • FUDGE (OGL and FUDGE System Trademark License; also under its own license)
  • vsM Engine

Creative Commons licenses

GNU licenses

  • Gods and Monsters (GNU Free Documentation License)
  • Circe (GNU Free Documentation Licence and GNU General Public License)
  • Fringe (OpenOffice Writer format) (GNU General Public License)

Other licenses

External links