The Freedoom project is a free content first person shooter game. It must be played with a compatible Doom game engine like PrBoom, Vavoom, or Odamex. Freedoom contains hundreds of original textures, sound effects and music tracks that can be reused royalty-free by Doom level authors and other independent game developers. The project provides three game packages, consisting of two single player campaigns and one set of levels intended for multiplayer deathmatch (FreeDM).

In 1997 id Software released the source code to their classic game, Doom, under the GNU General Public License. This means that the program code that powers Doom is free; Freedoom complements this with free levels, artwork, sound effects and music to make a completely free game. The game data is also designed to be used with much of the thousands of Doom levels and "mods" made by fans of the original game without the orignal Doom game data. If you have artistic skills (visual, musical, or maybe you just like making levels!) then you can contribute to this project!

Freedoom is liberally licensed under the BSD license - it can be re-used in your products and distributions. All that is required is that you include a short copyright statement that credits the Freedoom project.