Gesture Synth (gesture-synth.org)

This version converts hand positions and finger counts into musical chords using computer-vision hand tracking. You play chords by raising one to five fingers, and hand movement shapes tone and energy.

It runs entirely in the browser with no installation, and the site states that camera frames are processed locally and not uploaded. You can choose sound styles and record short clips for sharing.

Details below are taken from the site's own published description rather than hands-on testing.