Killing Floor is a mod of
Unreal Tournament 2004 based on
28 Days Later,
Resident Evil and other zombie movies. Killing Floor is a cooperative multiplayer horror modification set in London at present day. The basic idea of the mod is to help you and your mates fight through hordes of mutilated blood-thirsty zombies in order to survive till the next day. The mod also contains a single-player part, where you, a marine in the British Army, have to fulfil your missions in the blood stained streets of Kondon. It is mandatory to have a working and up to date installation of UT2004 before Killing Floor will run. Details can be found
here.