lwty.org - worksheets or practice exercises, calculators & answer sheets to engage the grade school...
SpeQ Mathematics - SpeQ is a small, extensive mathematics program with a simple, intuitive interface.
Free42 - Free42, an HP-42S calculator simulator
Qalculate! - Qalculate! is a multiplatform multi-purpose desktop calculator.
Calculator OSX App - Real Time.
NumWorks - The graphing calculator that makes learning math easier.