Airwave

Your right hand sets the pitch and snaps to a pentatonic scale so it is hard to sound bad; your left hand is the volume. Fingers pick the octave, a fist morphs the timbre, a pinch adds vibrato, and your mouth works as a wah pedal.

Hand tracking runs locally in the browser and the sound is synthesised in the page, so nothing about you leaves the machine. Desktop only — it needs a camera and a real amount of light.