Left 4 Dead

Left 4 Dead is a co-operative, survival horror, first-person shooter game by Turtle Rock Studios, who were purchased by the Valve Corporation part way into development. The game uses the Source game engine, and is available for Windows-based personal computers and the Xbox 360.

Left 4 Dead puts four human playable or AI-controlled Survivors of an apocalyptic pandemic against hordes of aggressive "Infected" (zombies). These Infected are controlled by an AI that dynamically balances difficulty and mood depending on the players' progress and situation. In an alternate game mode, human players can control up to four different Infected with special abilities and cooperate to stop the Survivor players.