DPlot - DPlot graphing software lets scientists and engineers graph, plot, analyze, and manipulate data.
GeoGebra CAS Calculator - Free online algebra calculator from GeoGebra: solve equations, expand and factor expressions, find derivatives and integrals
WinPython - The easiest way to run Python, Spyder with SciPy and friends out of the box on any Windows PC...
GnuPlot - Gnuplot is a portable command-line driven interactive data and function plotting utility.
SciDaVis - SciDAVis is a free application for Scientific Data Analysis and Visualization.
Giac/Xcas - Free computer algebra system