Howler.js
Javascript audio library for the modern web.
Tone.js
A Web Audio framework for making interactive music in the browser.
Wavesurfer.js
Navigable waveform built on Web Audio and Canvas
Vexflow
A JavaScript library for rendering music notation and guitar tablature.
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.
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)
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.
Wad
Web Audio DAW. Use the HTML5 Web Audio API for dynamic sound synthesis. It's like jQuery for your ears.
Audio.js
A cross-browser javascript wrapper for the html5 audio tag
Web Audio Api
The Web Audio API, developed by the W3C Audio WG
Alpha Tab
alphaTab is a cross platform music notation and guitar tablature rendering library.
Pizzicato
Library to simplify the way you create and manipulate sounds with the Web Audio API.
Tuna
An audio effects library for Web Audio, made by www.dinahmoe.com
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.
Teoria
A JavaScript music theory framework.
Jsmediatags
Media Tags Reader (ID3, MP4, FLAC)