Arma's fiesty little nephew, DayZ, hogs all the attention, but that doesn't mean Arma 3 sits on its haunches. In fact, with all of its military simulation scariness intact, Arma 3 is promoting a bunch of soldiers: to God. That's higher than a five-star general, I think, but I can't back that up with paperwork.
Developer Bohemia Interactive uploaded an hour-long demonstration onto its Twitch channel of the free multiplayer Zeus DLC. Zeus puts one player in the game master's seat, adding and removing gameplay elements on-the-fly. Apparently a lot of lightning is involved.
If you like beta testing, you don't have to wait to play Zeus. You just switch to the Arma 3 devbranch on Steam by right-clicking on Arma 3 in your Steam Library, going to "Properties," clicking on the "Betas" tab, and selecting the "Development Build." The game then updates. Afterwards, you can launch the game and search for a Zeus server — or create your own. To learn the basic controls of Arma 3: Zeus, Bohemia recommends you to play the "Zeus Showcase" first.
Arma 3: Zeus expects to go live early Q2 2014.