Maxima is a fairly complete computer algebra system written in lisp with an emphasis on symbolic computation. It is based on DOE-MACSYMA and licensed under the GPL. Its abilities include symbolic integration, 3D plotting, and an ODE solver.
Sage is a free open source mathematics software system spanning a huge range of mathematics including algebra, calculus, combinatorics, number theory and graph theory.
The Geometer's Sketchpad dynamic geometry software is an educational math software developed by KCP Technologies and published by Key Curriculum Press.
An encyclopedic collection of math games, problems, puzzles, and articles. A lot of math information for teachers, students and parents. Work out and enjoy mathematics. Explore unexpected connections. Even Word Problem Tutorials
The Math Forum is the comprehensive resource for math education on the Internet. Some features include a K-12 math expert help service, an extensive database of math sites, online resources for teaching and learning math, plus much mo...