On Monday July 19th Value games will release Free the game "Alien Swarm" complete with all of the source codes. The release will be on Steam. The game was created by the same creators of Left 4 Dead games and Portal 2.

You can visit the games webpage here: Alienswarm.com

Now a FYI if you have issues trying to play the game you might want to read this thread: "Steam" and "Value" brand games warning