Interactive mathematics
WIMS (WWW Interactive Mathematics Server) is a CGI Web application designed to host interactive mathematical educational activities such as exercises, computational math, and graphing tools.

Superficie
Superficie (surface) is a small program that allows to visualize 3D surfaces, and to have certain interaction with them. It allows to rotate, to move away, and to show illumination, on the surface at issue.

The ROOT System
ROOT - An Object Oriented Framework For Large Scale Data Analysis.

Yacas home page
Yacas (Yet Another Computer Algebra System) is a small and highly flexible computer algebra language. The syntax is handled by a infix-operator grammar parser. The distribution contains a small library of mathematical functions, but its real strength is in the language in which you can easily write your own symbolic manipulation algorithms. It also supports arbitrary precision arithmetic.