This is probably the use case you least expected to hear, but the first thing i thought of when playing with this is how useful it could be in helping make progress when learning jazz improvisation.

Typically when you're learning improv, you're figuring out what scales work with which chords in which parts of the harmony. Normally you'd start with something like 'xxx liked to use the half-whole diminished scale when leading into the I chord from the dominant', so you'd read that/listen to that bit of a solo, try to remember or look up the scale, practice it a bunch of times until you think you know the notes/fingerings, then try to use those notes in that part of your improvisation for that bar or two (while trying to not just play up and down the scale you just practiced playing up and down), until you eventually internalise the 'feel' of each of those notes in that scale in the context of that part of the harmony.

Of course nothing replaces practice, but that process can be quite offputting as you end up second-guessing a lot of your mistakes before your brain actually goes 'ahh that's what that's supposed to sound/feel like'. Conversely, the UX on this is so effortless that I just thought screw it, I'll try it for a couple of mins. I just drew some patterns, picked a transpose/tempo and hit play while I played the harmony part to something I was working through (spacebar mapping to play/stop/restart ftw, nice), and I ended up wrapping my head around it way quicker than I normally would, with a lot more energy left over. It made remembering/playing that scale by ear afterwards way easier too, was nice and quick to redraw the pattern to only include certain notes to focus on, etc.. Yeah, I probably didn't internalise as much of the muscle memory, but that's not always a terrible thing (stops you just playing up and down the scale), and the app also makes it super easy to save that context as a link in my obsidian notes so i can just come back to it whenever i want to pick up where I left off.

Honestly I was genuinely surprised by how well what you've made mapped to the use case. It kinda makes sense given how trad/bebop jazz improv is mostly just runs of notes of the same duration. Yeah ok it's probably not the only app for this, yeah it's probably not the best one, but it's the one that got me to do the thing I'd been putting off doing for ages, so I thought I'd share. Thank you for making it, really nicely done!