Math on a SMART, I mean Interactive White, Board

In a shout out to someone he calls the Northern Mathman, Geoff Day drew my attention to this incredible Java application for doing mathematics that is particularly well-suited to an IWB or tablet. Although it doesn't work quite as well for me as it does in this introductory video, with a little practice it could change the way I think about equations and mathematical calculations.

You can download it or use it directly on the web.