What would be cool is if you guys integrated Mathematica into Khan Academy. There is that new document format they introduced. For math it would be super useful to have the ability to really play with formulas directly in Khan Academy.
Mathematica may be overkill -- I suspect they'd just need something for basic symbolic manipulation, to reduce answers. In any case, a web-based mathematics system already exists; Sage can be run in a browser, and it integrates a number of useful mathematical features with Python:
