Many of you may have noticed people playing a lot of ArmaII lately. This is because of a mod called DayZ, which puts your player into a zombie apocalypse. You start on a beach in a mountainous area of Russia, with nothing except a bandage and a flashlight, and you have to scavenge guns, ammo, food and water in order to survive. Once your character dies in DayZ, you have to start again afresh. Zombies are not the only threat, you also have to look out for other players, they can be extremely dangerous (they want your beans).
All you need is ArmAII Operation Arrowhead, but I recommend you get combined operations as the mod will run a lot smoother with it. The ArmA Games are also pretty good fun if you're into sims or realistic shooters, but the controls can be a lot to get around.
ArmAII Combined Operations/OpArrow are currently on special-sale on steam. Nows the time to buy.