What's that? You want more free?

Well heck yeah, let's talk about Alien Swarm. Some guys from Valve made a dungeon crawler 4 player game but instead of a dungeon it's a space colony and instead of shields, swords, and magic, you wield smart guns.  I'm pretty sure the only thing getting this game to be sued by the owner of the Alien franchise is that the game is freeware. 

So get over to Steam and get this.