Mathics is a free, open-source 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.
Screenshots
mathicsscript: a text interface
mathicsserver: a Django-based Web interface
Download and install Mathics
Installation and Running Guide
Documentation
Support
Use the Google groups mathics-users for discussions regarding using Mathics and mathics-devel for discussions about development.
Wanted: Developers! Please get in touch if you want to be part of this awesome project.