Amplitudejs
A Javascript library that allows you to control the design of your media controls in your webpage -- not the browser. No dependencies (jQuery not required)
Timbre.js
JavaScript library for objective sound programming
Pizzicato
Library to simplify the way you create and manipulate sounds with the Web Audio API.
Audiolet
A JavaScript library for real-time audio synthesis and composition from within the browser
Waud
Web Audio Library
Teoria
A JavaScript music theory framework.
Tone.js
A Web Audio framework for making interactive music in the browser.
Wavesurfer.js
Navigable waveform built on Web Audio and Canvas
Buzz
Buzz is a small but powerful Javascript library that allows you to easily take advantage of the new HTML5 audio element. It tries to degrade gracefully on non-modern browsers.
Sound Manager 2
A JavaScript Sound API supporting MP3, MPEG4 and HTML5 audio + (experimental) RTMP, providing reliable cross-browser/platform audio control in as little as 10 KB. BSD licensed.
Vexflow
A JavaScript library for rendering music notation and guitar tablature.