howler.js : howler.js is an audio library for the modern web. It defaults to Web Audio API and falls back to HTML5 Audio.
sonicsquirrel.net : sonicsquirrel.net is a platform dedicated to netlabels and netaudio.
All music you find here is released under open licenses (mainly Creative Commons)...
Wavacity : A free and open source audio editor for the web derived from Audacity
librosa : librosa is a python package for music and audio analysis. It provides the building blocks necessary to create music information retrieval systems.