Do you remember Alien Swarm? Alien Swarm: Reactive Drop extends Alien Swarm, bringing more of everything: maps, aliens, game modes, guns and Steam Workshop support.

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-Tactical co-op for up to 8 players with a top-down perspective
-Steam Workshop support for community maps and challenges
-New co-operative campaigns
-Challenges: Modifications of the game, just like Mutations in Left 4 Dead 2
-PvP: Deathmatch, Gun Game, Instagib, and Team Deathmatch
-Singleplayer: Play with improved bots on all our official maps
-New Aliens: HL2 antlion guards and more
-New Weapons: Desert Eagle, Devastator, and Combat Rifle, and more
-Over 100 Steam achievements
-Leaderboards: compete with your friends for the fastest mission completion
-Improved spectating: see hacking minigames and mouse movements in real time