Doom -- "The Union Aerospace Corporation's facility on Mars is overwhelmed by demons. Only one person stands between their world & ours. As the Doom marine, you're here to do one thing - kill them all.
even though its just a mod for the chaingun, its preatty obviouse thats its more a complete new weapon. the gun can transform its shape by spliting up the barrel into 3 barrels which deliver an awesome power in the game.