This is cool! I read your article about musical faders some time ago as well [1]. It's great that you are thinking about what music can look like on computers in this free way.

[1] http://arthurcarabott.com/mui/

OP: you may want to post this to /r/musictheory on Reddit. I have a feeling it will be appreciated by the music geeks there.

That said, it is fantastic.

Really, really cool! What would be a nice feature, especially for longer rhythms, is highlighting the currently played syllable/phrase

Really cool.. Please highlight what is currently being played, will make it even better.

This is brilliant!!!

Did you record the sounds yourself?

Genius!