Freedoom is a project to create a complete, free Doom IWAD
file. Combined with the GPLed Doom source code, it creates a
completely free Doom-based game.
Information regarding Project Releases and Project Resources. Note that the information here is a quote from Freecode.com page, and the downloads themselves may not be hosted on OSDN.
While Freedoom has been in development for almost two years, this is
the first proper release. It includes a complete set of replacement
textures and a large number of sprites, sound effects, and other
material.