Zombie Panic! Source

Dive into the zombie apocalypse with Zombie Panic! Source (ZPS): a cooperative, survival-horror first-person-shooter. A fast-paced standalone modification. Choose your team as the Undead or a Survivor. Enjoy their unique abilities, weapons, and challenges in this action-packed mod!

The Teams

As a Survivor, unlock large arsenals of firearms, explosives and improvised melee weapons. Can you stop the waves of undead? Will you engage the horde head-on, or barricade and fortify while your friends play sniper? If all else fails, PANIC! Then run as if your lives depend on it… for they surely do.