PayDay: The Heist
http://www.youtube.com/watch?v=5tqnJ1vXUX8
4 player online co-op
Some info on wheather or not to get buy the extra stuff; if one has they can host maps they can host and everyone can join, also extra weapons aren't useful until you are quite high level.
http://www.reddit.com/r/GameDeals/comments/18428c/payday_the_heist_4_pack_is_on_sale_on_amazon_for/
Castle Doctrine, you set up traps and then go try to rob others houses
http://www.edge-online.com/features/jason-rohrer-on-dealing-with-permadeath-in-the-castle-doctrine/