Mathics is a free, general-purpose online computer algebra system featuring Mathematica-compatible syntax and functions. It is backed by highly extensible Python code, relying on SymPy for most mathematical tasks.
Sage is a free open-source
mathematics software system licensed under the GPL. It combines the
power of many existing open-source packages into a
common Python-based interface.
Mission: Creating a viable free open source alternative to Magma, Maple, Mathematica and Matlab