More info: http://dtex.github.com/canDo.js/.
canDo.js is a canvas wrapper for simple animations. It is ideal for animating UI elements (i.e. buttons with hover states). In a nutshell, canDo.js proxies the methods of the HTML Canvas 2D Context. It allows you to define a timeline, keyframes and easing functions.
canDo.js is distributed under the MIT License.