Welcome to Chernarus -- an open world post-Soviet state and one of the areas hit by a new and presently unknown infection which has wiped out most of the world's population. You are one of the few who have survived and now you must search this new wasteland in order to fight for your life against what is left of the indigenous population, now infected with the disease.

Designed on an updated version of the powerful ArmA II engine, this stand-alone version of DayZ takes everything that stunned players in the original MOD to a new level. Expect a more complex and authentic scenario (with more infected character types and more fully-modeled building interiors) that will immerse you in the survival horror like never before.

-IGN.com

DayZ Standalone is the much hyped follow-up to the DayZ Mod created by game developer Dean Rocket Hall. On 14 August 2012, Rocket announced that DayZ would become a standalone game that does not require Arma II. Development of the standalone version was headed up directly by Rocket, in conjunction with Bohemia Interactive, the publisher of Arma II. With this announcement, Rocket turned the mod version of DayZ over to the community for continued development. Some of the main goals for creating the standalone were to fix bugs and prevent hacking, two things very difficult to do under the previous Arma II architecture.

DayZ Standalone utilizes the Take On Helicopter engine, which is a branch of the Arma II Operation Arrowhead engine Real Virtuality. The engine has been heavily modified even including code from ARMA III.

-Gamepedia.com