It's a classic Treyarch map re-imagined for Call of Duty: Black Ops III's 2065 setting, Nuketown*. Originally a pre-order bonus, the map is a run-n-gun arena tweaked especially to highlight Black Ops III's chained-movement system and it's coming to all PS4, Xbox One, and PC gamers free of charge. In addition to the map, there is also the Nuketown* Personalization Pack available at no cost to the consumer. That pack drops with a Nuketown* themed Camo, weapon reticles, and calling card.
Now that it's free, Nuketown* has been added to the main map rotation, so expect to see it often in your multiplayer battles.
* Yes, yes I know it's supposed to be Nuk3town but sometimes I get fed up with that kind of juvenile number/letter replacement, especially when it makes the presentation of the word in anything but ALL CAPS look silly. I don't feel like yelling in all caps today or writing something that look silly. So it's 'Nuketown' in this article. Deal with it.