Mac OS X Softwares to Weapon Variety

Alien Swarm is a free-to-play, top-down cooperative shooter developed by Valve. Players control a squad of marines battling hordes of extraterrestrial enemies in various sci-fi environments, emphasizing teamwork and tactical gameplay.

Left 4 Dead is a highly acclaimed cooperative first-person shooter series where players team up to survive hordes of infected in a post-apocalyptic world.