Now there's a name I haven't heard in a while: Alien Swarm. The cooperative top-down shooter game, inspired by 2004's Alien Swarm Unreal Tournament mod, came out of nowhere in July 2010 and for a while grabbed everyone's attention.

　　Now, Alien Swarm: Reactive Drop is available for free on Steam. This is a version of the game expanded by a dedicated team of modders; arguably the most important addition is the support for Steam Workshop, which should allow the community to produce and share a ton of user-made maps and thus increase longevity by a significant amount.

　　Tactical co-op for up to 8 players with a top-down perspectiveSteam Workshop support for community maps and challengesNew co-operative campaignsChallenges: Modifications of the game, just like Mutations in Left 4 Dead 2PvP: Deathmatch, Gun Game, Instagib, and Team DeathmatchSingleplayer: Play with improved bots on all our official mapsNew Aliens: HL2 antlion guards and moreNew Weapons: Desert Eagle, Devastator, and Combat Rifle, with more to comeOver 100 Steam achievementsLeaderboards: compete with your friends for the fastest mission completionImproved spectating: see hacking minigames and mouse movements in real timeIn case you've played it already, let us know if it's still any fun.