The Khan Academy iPad app is coming along really well. We're getting near to a 1.0 release. This initial release will have video navigation and viewing as well as an interactive transcripts and offline support. Exercises will be coming in the next release. I've tossed a couple (very alpha) screenshots here. Huge thanks to +Adam Ernst
and +Jason Rosoff
for making this happen.
Support for other platforms (Android, iPhone, etc.) is coming soon, we wanted to get this first version out and people using it right away. The backend is written in a mixture of native code and HTML 5 (using jQuery Mobile). The full source code can be found on Github: https://github.com/Khan/khan-mobile