Need suggestions for CO-OP games with dedicated servers, preferably fps

I've been trying to play some coop games with a friend but so far we've always ran into connection problems. Neither of us has access to our routers so we can't port forward while hamachi and tungle don't work either.

We need some suggestions for coop (or vs) games to play together. We prefer first person shooters but any suggestion is more than welcome.

Thank you in advance!

PS: If this is wrong subreddit for my post please point in me the right direction.

Edit: We're on PC.

Edit2: Our systems aren't exactly top notch so newer games are out of the question, unfortunately.