Maxima - Maxima is a fairly complete computer algebra system written in Lisp with an emphasis on symbolic computation.

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.

MATLAB - A high-level language and interactive environment for numerical computation, visualization, and programming

SMath Studio - Tiny, powerful, free mathematical program with WYSIWYG editor and complete units of measurements support.

GNU Octave - GNU Octave is a programming language for scientific computing.

Function Analyzer - see the graph of a function