Did you ever need to plot a graph of a function but you didn't have access to your sophisticated mathematical software? With FooPlot.COM, you can do it in a few seconds. In fact, you can just add your function after the server name, e.g.
They also have a three-dimensional plotter - the quality is very limited here so far - and many new features are being developed.
See also scientific calculators in flash - SWF.