MATLAB - A high-level language and interactive environment for numerical computation, visualization, and programming
GnuPlot - Gnuplot is a portable command-line driven interactive data and function plotting utility.
Wolfram Mathematica - Mathematica has characterized the cutting edge in specialized processing—and gave the chief calculation environment to a large number of pioneers, instructors, understudies, and others around the globe.
GeoGebra CAS Calculator - Free online algebra calculator from GeoGebra: solve equations, expand and factor expressions, find derivatives and integrals
Maxima - Maxima is a fairly complete computer algebra system written in Lisp with an emphasis on symbolic computation.
Geometry Pad - Geometry Pad is a dynamic geometry application for iPad and Android tablets.