Petaporon is amazing!
I've been using it as a tool to prototype new music on, and desperately needed a way to download the music as MIDI to enhance later in other DAWs.
So I made a Petaporon JSON to MIDI converter: https://github.com/JoelBesada/petaporon-to-midi
It's a command-line tool for now, but if people are interested in a more accessible version (like a website), let me know and I might find some time to build it :)