NumWorks - The graphing calculator that makes learning math easier.
Jim - An overview of Jim capabilities
Rule of 3 Calculator - Apply the mathematical Rule of Three in an easier, faster and more practical way!
Insect - High precision scientific calculator with full support for physical units.
eMathHelp.net - Site is created to help people learn math. Includes algebra, calculus, differential equation calculators and notes with many examples.
errProof - The website has a lot of useful and unique tools.