I'm a day late and a dollar short with this, but I thought today we'd take a look at the DayZ mod.
For those unfamiliar with Day Z, it is an "open-world, persistent, PvP and PvE zombie survival mod"(PCGamer), for Arma 2. It takes place in a 225km^2 map, and features advanced AI zombies, while requiring players to make the decision to play the game alone, or to team up and try and survive with the minimal resources supplied, or whatever they can scavenge.
Arma 2 has been sitting atop the steam most popular games over the last week, and DayZ is definitely contibuting to this, boasting 48000 Unique users have participated in the Alpha.
I have not personally played the game, but I'll be buying ARMA 2 and installing this over the coming days (So expect a post about it in the coming weeks). Until then, PCGamer has been running an excellent series regarding the game itself, so give that a look.