I'm sure that a HN thread could turn up a bunch of great projects to follow.
I'll start:
Processing: http://github.com/jeresig/processing-js/
Python Plotting Library: http://github.com/astraw/matplotlib/tree/master
Python Physics Tutorial: http://github.com/llimllib/bitofphysics/tree/master
WYSIWYG Javascript: http://github.com/37signals/wysihat/tree