A 225 km2 open world post-soviet state wiped out by an unknown infection. Go Solo, team up with friends or take on the world as you choose your path in this brutal and chilling landscape using whatever means you stumble upon to survive.
Day Z is one of the most well known and ambitious mods to ever come out. Ironically it did so by abandoning lots of substance, and just dropping players into a Zombie-infected Chernarus with nothing to do but survive. Everything else is up to the player.
It's an interesting concept, and over time they expanded on survival elements quite a bit, but at least the last time I played, there wasn't enough teamwork emphasis. Custom Bandit skins were removed so people could kill others with no penalty, and they'd blend in perfectly. This plus the reduction of the amount of Zombies turned Day Z into Zombie Deathmatch.