Looking at their latest invention, Mark Cutler and Jonathan P. Howe will get an awesome job at some military aerospace company. They have created a quadrotor drone with variable-pitch, something that didn't exist before in these kind of machines. Not they can do some crazy acrobatics.
Go to minute 1:25 to see the cool action but, if you have time, watch the comparison at the beginning.
The variable-pitch propellers allow for more aggressive manoeuvres and aerobatics than possible with typical fixed-pitch quadrotors.
Full-sized helicopters have variable-pitch propellers, which allow them to do some aggressive maneuvers too. Their quadcopter is just the same and can do even more things. It can stop almost on the spot, fly upside down and basically move in any way you can imagine with absolute precision -- much more precise than anything invented to date.
Now I want one for my birthday. [Hackaday]