What other free coop games do you know?

[Dmitriy]

Are there any? Free to play also counts.
I know:
Team Fortress 2 new MVM game mode. It's basicly a survival mode, not campaign mode
Warface. Also free to play. FPS.

[Medavelvan]

Here's how to find free coop games on Steam:
Free Games on Steam!

Here's the most recent free game with coop I played: Alien Swarm

[Jormund]

I do not play a lot of free to play games, but I found Block 'n' Load a very fun game with friends. It just became a F2P title and I've had my fair share of fun moments.