Its based on a Unreal Mod, but here, you have a top-down 4 players co-op game. Alien Swarm adds 3rd person camera, depth of field, improved dynamic shadows and a wide variety of gameplay additions to the Source engine. Alien Swarm is a free game by Valve which you can download on Steam.

Along with the game get the complete code base for Alien Swarm that features updates to the Source engine as well as the SDK. Blaze your way through an overrun, off-world colony, eradicating the alien infestation in environments ranging from the icy planet's surface, to a subterranean lava-flooded mining facility. Plan your attack using an unlockable arsenal of weapons with countless loadout configurations against a wide variety of aliens. With your friends, form a squad of four distinct IAF Marine classes. Plan your attack using an unlockable arsenal of weapons with countless loadout Available free of charge, the game thrusts players into an epic bug hunt featuring a unique blend of co-op play and squad-level tactics. Summary: Available free of charge, the game thrusts players into an epic bug hunt featuring a unique blend of co-op play and squad-level tactics.

Download alien swarm steam