Great video with detailed paper which talks about flicking drones and some of the possible applications.
Swarming in the evening sky over a field, 10 quadcopters were instructed to form a circle. They are designed to communicate with one another to fly cooperatively, like birds in a flock, and they fell into line, each knowing its neighbor’s position. The technology is the first of its kind
Although I am not sure if this is the first of its kind (perhaps some of the particular details are a first), but swarming cooperative quads have been around for quite some time and here are a couple cool videos that you may/ may not have seen! Some of these videos use the vicon tracking system so its a little less impressive in the sense that the system provides mm accurate positional information at something like 250hz, but still fun to watch!
And a few more ‘Academic’ videos if the ones above where to ‘showy/artistic’ 
