BrainBread 2

BrainBread is a Source Mod for Half-Life 2 where the aim is to recreate a zombie attack. This is described as a cooperative multi-player game, however things go a little deeper than just gang up on zombies. When the game starts, all of the players are Humans that have to fight zombies in order to complete an objective in the map.
These objectives go from surviving an amount of time in a map, retrieving documents, killing an amount of zombies or reaching a certain place in a map. Of course, in the meantime there will be a swarm of zombies coming over you. There are AI soldiers that can help you defend yourself against the attack, but pretty much you and the other players are alone. Now it all seems like the same Zombie vs Human mod, but there is a twist. If a player is killed by a Zombie he will turn into one, and he has to kill two humans to play again as a human. This does encourage players to protect their teammates. The mod is famous for its GORE system in which zombie deaths are, well, gory. However, the amount of pieces and blood and action on the screen can make the screen sluggish in some systems. Overall the mod has gained a cult following since its Half-Life days, now with Source its just more fun.