FreeDoom is a Doom WAD file intended to be used instead of the copyrighted file from the original Doom and Doom II. The idea is that since the source to Doom is released as open source you can combine the free game engine with the free WAD to create an entirely free game. This also makes it possible to use all user-made WADs that require the original (and copyrighted) WAD by replacing it.
= External links =
[http://freedoom.sourceforge.net/ FreeDoom project page]
[http://www.samiam.org/slump.html Slump], a random map generator for FreeDoom