We were here series is decent
Killing Floor 2
Raft or most survival type games like The Forest
The Forest you'll spend good moments with your friends
Resident Evil 5 is arguably one of the best co-op games that there is.
CSGO coop maps by CTX
it's an absolute masterpiece mens)))
grim dawn, victor vran , path of exile
I liked the BF3 coop mode really much, other than that i would suggest payday 2
SRB2K, Very moddable version of mario kart for pc except it has a sonic theme.
- Fun for parties, mario kart like, Free, Easy to run, Easy to mod, You don't need to have the same mods to play online they automatically download.
- Setting up a server requires you to port forward.
- To really get the most fun you gotta spend some time downloading modded characters and tracks.
Enter the Gungeon is really nice co-op game