That's Falcon9_Mission20 first stage - after having reached 100 km, 5000 km/h, 16 km downstream, separating the second stage, turning around, and flying back - landing, vertically and under power, at Cape Canaveral almost exactly on the target.
As the first stage is approximately 70% of the cost of launches, this is a very, very big deal for space flight. With the upcoming launch of the Falcon Heavy - which has two of these as "boosters" around a third segment, all of which can potentially be landed the same way - we may actually see affordable major development in space.
