freedoom
http://freedoom.sourceforge.net/
Freedoom is a set of open-source freely redistributable game levels for Doom game engines. While ID software has released the Doom game engine under the GPL, they have not released the proprietary game files. Freedoom aims to produce a complete IWAD, or set of game files (levels, monsters, weapons, sounds) necessary to have a completely free/libre Doom game.
Freedoom is not yet complete. There are a few missing levels and monster sprites. If you would like to contribute to the Freedoom project then please visit the contributors page at http://freedoom.sourceforge.net/contributors.php . Contributors will also be interested in the yadex Doom level editor and the deutex wad manipulation tools that are also available from Fedora Extras.
Installation instructions
The freedoom package contains the game files only, but has a dependency on the prboom game engine. Freedoom may work with other Doom game engines, but so far only prboom has been packaged for Fedora Extras.
Running
Freedoom can be started using the desktop icon. You can also start it from the command line by launching the prboom game engine, which has been configured to use freedoom. More information on the various game options can be found in the prboom(6) documentation.
Configuration
Freedoom does not have any of its own configuration settings. Instead, you must configure the game engine prboom to set keyboard and mouse controls, difficulty levels, etc. These can also be configured in-game.