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.
Midi.js
Making life easy to create a MIDI-app on the web. Includes a library to program synesthesia into your app for memory recognition or for creating trippy effects. Convert soundfonts for Guitar, Bass, Drums, ect. into code that can be read by the browser. Supports multiple simultaneous instruments and perfect timing.
Teoria
A JavaScript music theory framework.
Sound JS
A Javascript library for working with Audio. Features a simple interface as the front end to multiple audio APIs via a plugin model. Currently supports HTML5 Audio & Flash.
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.
Audio.js
A cross-browser javascript wrapper for the html5 audio tag
Audio5js
The HTML5 Audio Compatibility Layer
Webaudio.js
web audio library for games
Tuna
An audio effects library for Web Audio, made by www.dinahmoe.com
Howler.js
Javascript audio library for the modern web.