Sage mathematics software
Sage is a Python based free open-source mathematics software system licensed under the GPL. It builds on top of nearly 100 open-source packages: NumPy, SciPy, matplotlib, Sympy, Maxima, GAP, FLINT, R to provide a common unified interface, either as a notebook in a web browser or the command line.
In addition to a local installation it is also possible to use SageMathCloud a free service with support from the University of Washington.
I’ve added Sage to the list of data analysis tools for Mac OS X.