Counter-Strike: Source - Zombie Riot Mod

                    
Grab your friends and get to fight waves upon waves of undead horrors. This mod brings a Killing Floor like experience to CS allowing you to configure how many zombie waves, the amount per wave, and the statistics of the zombies you are fighting. If you happen to have no friends, that's okay too as you can use bots to replicate the experience of mowing down zombies with your pals.