Rough.js is a light weight, stand-alone Canvas based library that lets you draw in a sketchy, hand-drawn-like, style. The library defines primitives to draw lines, curves, arcs, polygons, circles, and ellipses. It also supports drawing SVG paths.
Check out the website: roughjs.com
The latest Rough.js release (beta version 0.1): Download
This project was inspired by Handy, a java based library for Processing. Rough.js borrows some core algorithms from Handy, but it is not a JS port for processing.js.