BounceBud for iOS and Apple Silicon Macs is a physics-based MIDI generator app. It has 4 customisable keyboards on each side with their own MIDI outs. The way it works is that when a ball collides with a keyboard, the keyboard plays that note. Ball count, speed, and size can be changed with the knob controls.
Pricing and Availability:
$4.99 at the app store.
And Dreadbox Hypnosis, Circuit Tracks
Cheap as chips too
Monster Poly actually portable
The new official emulation, endorsed by Oberheim