Earth-Defense-Forces -/EDF/-

The Co-Op game Alien Swarm is now out on steam for free. The original game was developed as a modification for Unreal Tournament.
Valve Software (Half-Life Series, Counter-Strike, Left 4 Dead Series, Team Fortress 2) hired the mod-team and released the game
on the Source Engine, including all tools that are needed to make new maps and/or modify the game itself.

Game Facts :

-Tactical, 4 player co-op action game with a top-down perspective
-Complete game code and mod tools
-Unlock persistent items by gaining levels
-Over 40 weapons and equipment with countless loadout configurations
-4 unique classes and 8 unique characters
-Matchmaking, Steam Cloud, Steam Stats
-64 achievements
-Tile-based map generation tool
-Powered by Source and Steam