Fascinating project on Kickstarter: really worth supporting:
What is Vectr?
The Hackme Vectr is an entirely new and unique way to interact with a modular synthesizer. Vectr is a three dimensional control interface designed for Eurorack modular system. It senses the location of a hand over its face and outputs a signal proportional to position for each axis: x (left and right), y (up and down), and z (in and out). So, you can control three things at one time, like turning three knobs all at once by moving your hand through the air.
via Vectr – Open Source 3D Sensing Gesture Controller by Matt Heins — Kickstarter.