You meant https://poly.ozieblowski.dev/ ? (generatorpoly.ozieblowski.dev doesn't work). It's neat.

Web MIDI clock is still a mess AFAIK, so MIDI sync in the browser seems far away. This tool doesn't really have a concept of tempo so it would probably not benefit much from syncing (except maybe for receiving start/stop?)

But you can do a lot of things with MIDI notes, including using them to drive filters, etc. so you can totally use this to modify an existing piece on another MIDI instrument, live.