I always loved Mathematica for its symbolic architecture, and that power is now freely available online through the stunning Wolfram|Alpha computational engine.
In these days, I'm studying for the third calculus course and I'm using Alpha extensively for definite integration. When I heard 'bout Wolfram's Alpha widget builder I felt natural to develop an on-line integral calculator.
It's simple indeed, but very nice. Too bad our university's facts knowledge base is too short, because I can't imagine any killer application for the website yet. I contacted the Wolfram labs, in order to extend it a bit. One day, who knows...
