ArmA II is Just Giving Itself Away. For Free. Sort Of.

ArmA II, one of the best war games money can buy, is now giving away half of itself for free. Charity!
Develoeprs Bohemia Interactive announced yesterday that the ultra-realistic shooter and sim will have its multiplayer component released for free later this month. You can even build and play custom singleplayer missions.
The game's campaign mode and mod support (along with better-quality textures) will be withheld from this version, however, and only available if you want to pay for the full game.
So think of this as one of the world's biggest demos and you'll be fine.

Source:http://kotaku.com/5810620/arma-ii-is-just-giving-itself-away-for-free-sort-of