Could be a useful learning tool. Works in Chrome and Firefox, not on IE and Android.
Musical Keyboard - JS Dynamic Audio Synth
This is a an emulated keyboard (a synthesizer!) that spans three musical octaves (C3-B5).
keithwhor/audiosynth @ GitHub
Generate musical notes dynamically and play them in your browser using the HTML5 Audio Element. No static files required!"
This could be combined with simple text notation for music notes to also record and play music from web.
GUIDO music notation - Wikipedia, the free encyclopedia
Guido Music Notation - CCARH Wiki