MIXelleTypeScript, YouTube API, Spotify APINo Spotify premium? No problem! Make playlists to shuffle the way your heart desires.
PitchyTypeScript, TensorFlow.js, VexFlow, Basic PitchTurn audio into sheet music with note names - for people who can't read music (me).
FlashNightTypeScript, Web Audio API, Canvas 2DReal-time audio visualizer (warning: maybe bright lights).