Yes, the DayZ developers are currently working on a standalone game, but until that game comes out, many are addicted to playing the current version. DayZ, as it currently stands, is a mod that is played in conjunction with ARMA II: Combined Operations. If you've ever tried to play the mod, then you may have had to go through a few hoops and downloads to get it working.
Those who felt setting up the mod was a pain, or simply couldn't get it running before, can now rejoice. Today the DayZ mod has made its official debut on Steam. Mods were introduced to Steam years back but it has been a while since a hugely anticipated one has been made available.
What does this do? Basically, all the hassles of servers and installing secondary programs are over with. Instead, you simply need to run Combined Operations once, then run DayZ through Steam. Then, the mod should just work! Oh, and in case you are confused, this game is in no way related to The War Z which is a game with a fairly storied history.