Crafty.js
“An open source beta JS Engine.”
Crafty is a nice 2D HTML5 Game Engine under active development with a small footprint (14.5KB compressed) that projects a jQuery-like syntax instead of a more traditional classical inheritance model. This plays to Javascript’s strengths – Javascript doesn’t have classical inheritance model after all – and is a great differentiator from other engines. Instead of long chains of inheritance it’s built on a “Entity Component System” where sprites (called Entities) are manipulated by adding reusable Components to them.
Check out our in-progress Crafty.js Tutorial