It's out on steam for pre-purchase, doing so is a free ticket to the alpha, and beta. http://www.arma3.com/ It's only an alpha, and it already has the modding community on it, making missions for the sandbox mode, and mods for ease of use. Guys, this game is currently very fucking buggy(alpha build), but its also very fucking fun, seriously, play it with your friends.
its not very short on content, either. http://www.youtube.com/user/Dslyecxi has a whole bunch of vids on it, hes not actually a developer, but he is doing a lot of the PR for them.