Fact Flow - Simple solution to help kids achieve math fluency
NumWorks - The graphing calculator that makes learning math easier.
Paperspade - Type math easily through just English text!
Learney - Knowledge aggregator for developers
Scoby Social - A safe place to co-create
eMathHelp.net - Site is created to help people learn math. Includes algebra, calculus, differential equation calculators and notes with many examples.