Hey guys, I've tried Deceit-F2P
http://store.steampowered.com/app/466240/Deceit/

You really need to know what you're doing to survive. Eventhough f2p, it's not an easy game, so i'll cross this out.

So the remaining good f2p Team Fortress 2 and

http://store.steampowered.com/app/563560/Alien_Swarm_Reactive_Drop/
8 players

see if you'll like these

http://store.steampowered.com/app/204360/Castle_Crashers/

let us know if there are other good coop games