There are quit a few alternatives to Matlab: GNU Octave, Scilab, freeMat, and Sage. They all have their advantages and disadvantages. But at least there is one suiting your needs. Currently I am looking at Sage, which seems a “confederation” of multiple GNU math libraries. What interested me most is its web based worksheet allowing multiple users to share and collaborate. Here is a screenshot:
The full content of this “test” worksheet is here
If you are using firefox, accept the warning.