License: GNU GPL 1 or 2
Distributed under the GNU GPL license (ver. 1 or 2). Free to use for any purpose, study, improve, and redistribute. Not free to restrict said freedoms
Alternate name: GNU General Public License
The first video game about License: GNU GPL 1 or 2 was released in 1987.
Generally GPL is unsuitable for text, art and other non-source code media that is separate from the application. GNU FDL or other licenses are recommended for such instead (as in, application to them is vague in terms of legality). However, art, text, and files distributed within executables and source as a single unit are GPL by default as well. For them to use a different license that is not compatible with the GPL they must be distributed as a separate entity.
Games can begin life under the GPL license, or be switched to the GPL from a proprietary license or other another open source license. Please add the tag for the other license and license-changed in such cases. Some times, source code for commercial games under a proprietary license are published via the GPL while content remains non-free. Please indicate the proprietary nature of the content in those cases
GPL version 3 includes clauses that make it fundamentally different from versions 1 and 2 which may have important effects for gamers and is therefore a separate group
Public Domain code and GPL code can be mixed together in variety of ways. A copyright holder of GPL code can change their license to Public Domain. But someone else cannot change a code's license to Public Domain if they are not the copyright holder. ie: The Free Software Foundation is the copyright holder for GNU Chess (GPL licensed code). I can make a Deep GNU Chess game using their GPL code. Deep GNU Chess cannot be Public Domain because it uses code that The Free Software Foundation owns. Neither can I say that just the bits of new code that I created are Public Domain. Because my code modifies FSF's code, it therefore becomes their code under the terms of GPL. Note that clauses in GPL version 3 may actually allow GPL3 code to be made Public Domain by someone who does not own the copyright. If someone claims Public Domain for modified or used GPL1 or GPL2 code, and is not the owner of said code, license-contradictory applies.