FreeDM is a fast-paced competitive deathmatch game, part of the Freedoom
project. Rather than the usual single-player focused levels, these
contain no monsters and are intended for deathmatch only. It is
compatible with mods for Doom II.
The Freedoom project aims to create a complete free content first person
shooter game. But Freedoom by itself is just the raw material for a
game: it must be paired with a compatible game engine to be played.
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.