Calculator OSX App - Real Time.
SpeQ Mathematics - SpeQ is a small, extensive mathematics program with a simple, intuitive interface.
Real Time Calculator - A practical browser calculator that outputs results in real time!
NumWorks - The graphing calculator that makes learning math easier.
Qalculate! - Qalculate! is a multiplatform multi-purpose desktop calculator.
PCalc - PCalc is the powerful choice for scientists, engineers, students, programmers, or indeed anybody...