These libraries aim to wrap the Canvas element and extend it one way or another. Some focus on making it easier to use while others add extra functionality as well.
undefinedThese applications use Canvas one way or another:
CanvasDraw - Sketching application for RateMyDrawings. Requires registration.
Harmony - Mr Doob's famous procedural app.
kMOD - Harmony fork.
Muro - Sketching application for DeviantArt.
rhyolight's Harmony fork with some mods by bebraw - Some extra brushes + mirroring features.
Sketchpad - Sketching application.
Pinelo - Facebook Procedural Drawing App. Needs Facebook account.
Walma - Collaborative whiteboard. GPLv2+
Picozu Editor - Online photo editor
Canvas Cycle - Old Skool color cycling demo
html2canvas - Screenshots with JavaScript
node-canvas - Implementation of Canvas in Node.
escapes.js - Renders ANSI art