There's a mod for ARMAII called DayZ. There's also the new standalone, which is in its Alpha stage. Read about it yourself instead of asking us to spoon feed you.

It's [i]technically[/i] in the Zombie Survival genre, but in reality, it's other people you need to watch out for- the zombies are just a nuisance. It is NOT a game for everyone. The controls are significantly more complicated than what most people are used to, and it can take HOURS for anything exciting to happen. That, and it's very difficult. You can starve, die of thirst, die of blood loss, fall down stairs and break a leg, get killed by other players without ever seeing them- along with a hundred other infuriating things. You also lose everything when you die- Clothes, food, weapons, tools, medical supplies, map progress- EVERYTHING. That being said, it's the difficulty and hours of monotonous walking that make Player to Player interactions so intense and exhilarating. Is he going to shoot you? Should you shoot him first? You can never tell who's trustworthy. Some people are generous, some people shoot on sight. [i]Some[/i] people are absolutely methodical and pretend to be your ally for hours (or days) before betraying you, handcuffing you, and force feeding you disinfectant until you die. You never knows what's going to happen. That's what makes the game great! If you think you're up for it, grab a couple pals and hop on. Whether you play the Mod or Standalone is up to you, but right now the Standalone is in Alpha so it's missing a lot of content (i.e. vehicles, weapons, bugfixes), so the Mod is a better, more complete option.