On the steam market place there is a free to play game called No More Room in Hell (NMRiH) it goes up to 8 player co-op and there are survival based maps and objective based maps. Its like a combo of DAY-Z and Left 4 Dead. The zombies are like George A. Romero type zombies. All you need is a steam account and 6-7 gbs free space. If anyone gets it let me kno so we can play