The yogscast did a playthrough of this game, DayZ. They weren't taking anything seriously, just like any other game, but people seemed to be angered by that same fact. 

Apparently Day Z is a hardcore game set in a Russian countryside where a zombie apocalypse broke out. You can only play in PUBLIC OFFICIAL servers with other player where they can either choose to team up or be savage bandits....

Thats all I know. Can you guys tell me more in detail what this game is? Im a HUGE fan of the walking dead and I really want to be sure that I would love this game when I decide to buy Arma 2: CO for this mod. 

Basically that a "Zombie Survival "Horror" mod", I've heard it's pretty darn good so I wish I could try it myself.

It's a game where you lure other players to exposed places in order to kill them and steal their gear and/or rake in the Youtube views.

http://www.youtube.com/watch?v=ru5RglF-I3E

I think there are friendly players and bandits. I dont think everyone is an asshole in this game.

http://www.youtube.com/watch?v=4LfA-7KePN4&feature=relmfu 

Very cool mod. Take the beans and run!

it's zombie u for hardcores

I seen my cousins play it and to be honest I wouldn't touch this game for another few months, it seems very buggy and zombies walk through the environment. I know it's in beta and that's why I'd wait.

....
its a mod for the PC game ARMA II
the idea is a zombie apocalypse but the game is very realistic. you need for get food and water. players can kill each other and if you die you lose it all. weapon noises attract zombies and the idea is for it to be a realistic apocalypse.
compared to every zombie game out there the DayZ mod is the most realistic example of what would happen in a zombie apocalypse

Actually looks decent, why hasn't something like this truly been developed?

Because IMO it would be the perfect game, I could see myself playing nothing but this until say, a sequel came out! Can't be good for profits right? :P

I just overall love the idea of an open world, multiplayer, hyper-realistic, post-apocalyptic survival game. And the fact that they threw zombies into the mix overall just makes it that much more awesome.