Cocos2D-html is an HTML5 port of the popular Cocos2d-x library, enabling you to make games that run in a browser, using a syntax that works virtually unchanged on a number of platforms.
You can download the source as a zip right here.
The project is also available on GitHub.
In anticipation of this release, the Cocos2D tutorials on this site where all updated to the new API, so should work unchanged. There were some pretty major changes in the API as detailed here.
Finally, there have been a series of Cocos2D related books published that could prove helpful in puzzling things out. ( Of course, start with the tutorials! ).