SpeQ Mathematics - SpeQ is a small, extensive mathematics program with a simple, intuitive interface.
NumWorks - The graphing calculator that makes learning math easier.
Qalculate! - Qalculate! is a multiplatform multi-purpose desktop calculator.
Learney - Knowledge aggregator for developers
eMathHelp.net - Site is created to help people learn math. Includes algebra, calculus, differential equation calculators and notes with many examples.
Calcbot for Apple Watch - Calculate, convert, and split tips from your wrist