2d javascript graphics
Did you ever wish that you could draw lines or circles in html? Without using images. Now you can by using the javascript graphics classes. They were written by Walter Zorn and can be downloaded here.
Workflow Javascript API
But if you think that is cool than you need to have a look at the Draw2D website that actually contains an api for making workflow programs. It handles dragging and dropping, arrows boxes. Every thing you need to make a workflow program. The api is actually very well written and I have used it in previous projects. It's completely object oriented javascript and quite cool.
3D rendering in Javascript
The last really cool website contains an explanation on how to render 3D images using javascript and html. Just read the explanation and have fun using it.