Here is a cool VR game that lets you use your hand to finger paint music in the air. It uses a VR headset, Leap Motion Controller, and Orion software:
Low notes are near the ground and they get higher pitched as you race your hands upwards. Once you have painted a brush stroke into the air, that instrument will loop allowing you build up tracks.
To stop a track, you can dip your left hand into the source paint bucket. More info is available here.