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. Requirements 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 is 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 those players (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), which is a version of the system containing only the Open Game Content, without any Product Identity.
  • 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.

Some open games, despite being free to use and modify in derived work, require you to buy a printed book or PDF copy to learn the rules. The list below should only contain examples of systems that are also 100% free to acquire digitally - or at least allow you to look up most of the rules online.

Open Game License

Note that the official d20 Trademark License, designed for use with D&D 3e SRD, has been revoked, but D&D 3e SRD was not. Although it can still be used, many companies and the community at large has given preference to Paizo's Pathfinder SRD, which is compatible with most of previous d20 material, and still receives updates and support from the publisher. While the D&D 3e SRD is no longer supported or updated, because Wizards of the Coast has focused efforts on the D&D 5e SRD.

Since "perpetual" (no specified end) does not mean "irrevocable" (can not be cut short), the OGL can be revoked at any time. This creates a debate over whether or not an "OGL" game is truly open.

d20 System-based

d6 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

Creative Commons Attribution

Creative Commons Attribution Share Alike

Creative Commons Attribution Non-Comercial

Creative Commons Attribution Non-Comercial Share Alike

GNU licenses

'Copyright Free'

These works are generally free to be used commercially, without attribution, and without requiring derivative works be shared under the same licence (copyleft). Works are typically placed here because: 1. their copyright term has ended; 2. their author placed them into the public domain; or 3. their author gave them a licence that allows them to be used effectively as public domain.

Other licenses

FUDGE License

The FUDGE license is a short copyleft non-commercial (except for when bundled with a larger periodical) license used by FUDGE before April 6, 2005, when it was changed to use the Open Game License.

  • FATE 1e
  • FATE 2e - also the twists and Pyramid Reloded expansions are dual-licensed under the FATE license and the OGL (there's also a FATE 2e SRD licensed under OGL, see its section).

External links