Get LMS 1
(last man standing)
It has Single PLayer level, that are multiplayer modded (very buggy)
And they have maps that are multiplayer that you have to work together to kill waves of endless enemies. Also what is neat, is if you get a high score, the server saves it, and it is displayed at the end of the game.
This is by far the best mod i have seen for doom 3
http://lms.d3files.com/index.php
Doom 3 Mod 
Linear Mode
