Alien Swarm is a multiplayer top-down shooter video game developed by Valve. It is a remake of a mod for Unreal Tournament 2004 and it was developed by the original team who were hired by Valve during the course of the development process. Alien Swarm is a top-down shooter where four players can join a single co-operative game the aim of which is to progress through science fiction-themed levels while eliminating waves of aliens. Players can choose from 40 different pieces of equipment ranging from weapons like assault rifles to grenade launchers and offhand items like mines and healing beacons. The game includes persistent statistics unlockable equipment and achievements.