WebSplat is a browser-based jump-n-run platformer game that works on any web page. It converts the existing page into platforms, then adds its own sprites and other game elements.
The best way to try WebSplat is probably the canonical WebSplat game at http://websplat.bitbucket.org/ . If you want to make your own game or otherwise make modifications, here's how:
Check out the source and data. The data is not stored in the source repository, it is available elsewhere.
Start a web server to refer to it. http://code.google.com/p/mongoose/ is an easy choice.
Use the following bookmarklet:
When you have it working, it should be easy enough to figure out how to modify loader.js, websplat.js and the bookmarklet to refer to your new instance.