-= Gametoast.com =-

So is there a co-op Half-Life 2 for PC? If so how does it work.

http://synergymod.net/

A Half-Life 2 mod, but it requires that you have Half-Life 2 in the first place.
I don't have it personally, maybe some other people can tell you more about it.

Synergy is pretty fun and has a lot to it, so I couldn't just explain how everything worked very easily. I personally like Follow Freeman better, although they haven't implemented the Half-Life campaign into a public version as of now.