There is strength in numbers, even when it comes to drones.
Scientists at the ETH Zürich university studying the flight of drones have 3-D printed some drone airframes and jammed them with electronics that allow them to sense each other's presence. In flight, individual drones are unstable, but when hooked up to each other magnetically, they can create a single unit that flies almost flawlessly.
Perhaps the truly interesting part of this system is that when the drones are connected in fight, the computing tasks needed to keep them flying--like balancing thrust from each motor--are distributed across each individual drone's electronics system.
The flying swarm was developed to display this kind of distributed computing, and also as an art demonstration of robot tech. Flying swarms have been an interesting research topic recently, with studies into how they can fly in a coordinated manner, and even how they can collaborate to complete big tasks like constructing whole buildings.