This is a Markov Chain based generative arpeggiator. It stochastically walks through diatonic chord changes using weights derived from Hook Theory's database of chord change trends in popular music. For each chord, it randomly selects notes from three octaves of arpeggios. It's sort of like an infinite music box.
I like it. Believe it or not, it took me a while to find the play, to my frustration, as without pressing it, nothing else is clickable, draggable, etc.