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

iPython - iPython provides a rich toolkit to help you make the most out of using Python interactively.

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.

Python - Python is a clear and powerful object-oriented programming language, comparable to Perl, Ruby, Scheme, or Java.

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

bpython - bpython is a fancy interface to the Python interpreter for Unix-like operating systems (I hear it...