Tone.js
A Web Audio framework for making interactive music in the browser.
Flac.js
FLAC decoder in JavaScript
Wad
Web Audio DAW. Use the HTML5 Web Audio API for dynamic sound synthesis. It's like jQuery for your ears.
Timbre.js
JavaScript library for objective sound programming
Howler.js
Javascript audio library for the modern web.
Pizzicato
Library to simplify the way you create and manipulate sounds with the Web Audio API.
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.
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.
Alpha Tab
alphaTab is a cross platform music notation and guitar tablature rendering library.
Speak.js
Text-to-Speech in JavaScript using eSpeak
Teoria
A JavaScript music theory framework.