Alien Swarm is a game that started out as an Unreal Tournament mod has become a full blown Multi-player shooter game now which just released in it’s entirety, including the SDK, on Valve on Steam.

Alien Swarm is a futuristic, top-down, first person tactical shooter game that permits up to 4 participants join a single accommodative game, with the objective to advance through science-fiction themed levels defeating waves of aliens with a choice from a 40-strong armoury of weapons. The game includes relentless statistics, unlockables and accomplishments.

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. With your friends, form a squad of four distinct IAF Marine classes. Plan your attack using an unlockable arsenal of weapons with countless loadout configurations against a wide variety of aliens. 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

In addition to the Alien Swarm Multi-Player Shooter Game, Valve has also released the complete code base for Alien Swarm which includes updates to the Source engine SDK and full Steamworks integration.