Alien Swarm

This is probably one of the most popular free to play co/op games out on the market. It's exactly what it sounds like, you play against aliens that swarms in. You are supposed to take yourself from point A to point B without getting killed. You can weld doors togheter to make the aliens stay outside for a while. I think this game is excellent it's a perfect co/op game it's on steam and it's free! So if you are sitting with a couple of friends on skype or if you are at their place playing a game this is absolutly a game I would recommend! You can play solo too but it's way more fun to play co/op. So if you havent played this game so far, do it! It's totally worth the waiting, and it's free!

Check it up on the link below the picture
The rating is 9/10

http://store.steampowered.com/app/630/

http://www.alienswarm.com/