Drawingboard.js
A canvas based drawing app that you can integrate easily on your website.
Rimg
A responsive image solution for browsers that support mediaqueries. Pure javascript and no server-side code.
Liquidfun
2D physics engine for games
Obelisk.js
JavaScript Engine for Building Isometric Pixel Element with HTML5 Canvas
Jcrop
Jcrop (official) - Image Cropping Plugin for jQuery
P5.js
A JS client-side library for creating graphic and interactive experiences, based on the core principles of Processing. http://twitter.com/p5xjs —
Ocanvas
JavaScript library for object-based canvas drawing.
Color
JavaScript color conversion and manipulation library
Gif.js
JavaScript GIF encoding library
Soc.js
An easier way to create social icons
Img to Ascii
A JavaScript implementation of a image to Ascii code
Breathing Halftone
Images go whoa with lots of floaty dots
Focal Point
A small set of CSS classnames to help keep images cropped on the focal point for responsive designs. Using only HTML/CSS, web authors can specify an image's focal point, which stays as the image's primary focus, while the image's available width changes on responsive webpages. Crop and re-size images depending on available width and let CSS to do all of the work, and without any JavaScript.
Paper.js
The Swiss Army Knife of Vector Graphics Scripting – Scriptographer ported to JavaScript and the browser, using HTML5 Canvas. Created by @juerglehni & @jonathanpuckey
Easel JS
The Easel Javascript library provides a full, hierarchical display list, a core interaction model, and helper classes to make working with the HTML5 Canvas element much easier.
Html2canvas
Screenshots with JavaScript
jQuery QR Code
qrcode generation standalone (doesn't depend on external services)