I am looking for web apps for symbolic and numerical mathematics.

I am not interested in what could be considered advanced (pocket) calculators and I know that Google search and Wolfram Alpha can also be used for many types of calculation.

I am thinking of apps with capabilities similar to that of Maple/Mathematica/Matlab/Octave and so on. Not that they have to be *that* advanced, but some kind of worksheet with input/output, simple scripting (for loops, etc.) should be available. Plotting would also be nice.

I realize that such an app would require a lot from the servers (if many users where doing heavy calculations) but maybe somebody have found a solution?

The apps that I have found so far are these:

* An [online version](http://sciencesoft.at/bc/) of GNU's bc (they call it a demo, however).
* [Sage Notebook](http://www.sagenb.org/). Looks very promising.

Open source projects are preferred, even if not in a "mature" state.