https://instrument-practice.netlify.app
When you have a new instrument, you might not know where all the notes are. I just bought myself a button accordion and I'm very rusty.
This web app shows you a note and asks you to play it. It uses a monophonic pitch tracking algorithm to figure out which note you're playing. If you get it right, you get a new note.
You can set the range of notes for your instrument using the controls on the page. If you play a note outside of the range it won't show up.
Pitch tracking is handled by the Web Assembly bindings of Aubio's implementation of Yin. It's not perfect, but works well enough for some instruments.