It's online. It's basically GTA. It's awesome. It's for PC only and the current beta is for EU users only (NA people may join but your pings will suck, sorry!). Can't say more due to the NDA, but I've got three invites to give out! Just post a comment if you want one and I'll PM you with the code and instructions.
If you need more infos, check the official site http://www.apb.com/