Alien Swarm is a totally free game from Steam that focuses on online cooperative games.
It's really fun (and free) so if anyone is interested in checking it out we could create a little TUS group of players and have some games from time to time.
Game is class based top down shooter, there's Sargeant, Special Weapons, Medic and Tech classes, each of one has two different characters with different stats, you level up and all that stuff, items to pick up, weapons bla bla...
You need to download steam, make an account and download it through the client, it's fast, it'll download as fast as your line can handle, and it's only 2 GB.
Anyway, video: