GeoGebra CAS Calculator - Free online algebra calculator from GeoGebra: solve equations, expand and factor expressions, find derivatives and integrals
GnuPlot - Gnuplot is a portable command-line driven interactive data and function plotting utility.
Giac/Xcas - Free computer algebra system
GNU Octave - GNU Octave is a programming language for scientific computing.
Graphing Calculator - Visualize equations and functions in 2D, 3D and 4D.
MATLAB - A high-level language and interactive environment for numerical computation, visualization, and programming