classic_doom_3_0.56 ?

[Penkster]

Slightly off the topic but this mod is another very good one to get.

Last Man Standing Coop Mod is a Doom 3 Coop Single Player and Multiplayer modification that aims to bring back the classic Doom experience.

http://lms.d3files.com/

You can play the original Doom3 maps, the ROE maps, Classic Doom and the LMS maps all in glorious co-op mode, makes for some fun with one or two friends.