I made a drum machine that I think is pretty cool - https://main.d28ilu31tegyi1.amplifyapp.com/ I taught myself how to program 15+ years ago because I wanted to make music software. Fast forward 15 years, and I've spent my whole career as a designer for B2B Saas. I wanted to re-learn some development stuff and going back to my original inspiration seemed like a good idea. (Still a bit in progress and sorry doesn't work on mobile, there is some Web Audio stuff I haven't figure out for mobile yet)
I also built a small app to learn my piano chords. You can play along with a MIDI keyboard. https://www.learnyourchords.com/