Peint is a modular, event-based, asynchronous canvas-rendering library.
Wow, that's a mouth full! What does it all mean? It's awesome, that's what!.

It also means you can do complex rendering tasks very easily.
You can render text, images and shapes using pixels OR percentages,
and best of all; you can use relative origins like "right" and "bottom"!

Infact, this whole page is rendered using nothing but Peint!
The real action is in /js/init.js and the modules are well commented.
Trying downloading the source to see how it works.