A 3D hair cutting machine.

It would allow someone to have their head scanned by a laser or series of lasers to get the exact shape of the scalp. They could import the scan on to a computer, which would allow them to perfectly model the hair cut they want in 3 dimensions, which would then be set back to something akin to a hair C&C machine that would suction all the hair outwards and then cut it according to the model designed on the computer.