HTML5 Audio API

Several years ago this wasn't really possible without Flash. A fully functional sound spectrum visualizer player made fully in HTML5 and JavaScript/WebGL

3D audio spectrum visualizer

3D audio spectrum visualizer

3D audio spectrum visualizer

A web based piano made with HTML5/JavaScript. Well done!

HTML5/JavaScript piano

Old timer russian radio replica made with HTML5 and JavaScript

Old timer russian radio device replica.

Meow Peow player in a browser

Fully functional MP3 player in a browser.

Links:
https://developer.mozilla.org/en-US/docs/Web/API/Web_Audio_API
http://webaudioapi.com/
http://shop.oreilly.com/product/0636920025948.do
https://developer.mozilla.org/en-US/demos/detail/beyer-music-player/launch
https://developer.mozilla.org/en-US/demos/detail/oscillators
https://developer.mozilla.org/en-US/demos/detail/musical-mines-and-rails
https://developer.mozilla.org/en-US/demos/detail/touch-turntables
https://developer.mozilla.org/en-US/demos/detail/classical-music-jukebox
https://developer.mozilla.org/en-US/demos/detail/soundbox-lite
https://developer.mozilla.org/en-US/demos/detail/html5-piano