[mR] Forums

You can download the free version which is just a multiplayer launcher, no singleplayer.

But to play DayZ you need to own Operation Arrowhead, which is in effect, an addon for Arma 2/ Arma 2 Free.

Operation Arrowhead works with the free version so you can save some money buy just buying OA instead of Combined Operations.

Rocket said that soon you wont be able to play with Arma II Free, it's best to buy Combined operations anyway

Well the only reason you need Arma II/Free is for Chernarus and the player models, so that shouldn't matter I don't think