SpeQ Mathematics - SpeQ is a small, extensive mathematics program with a simple, intuitive interface.
Numi App - Numi is a beautiful text calculator for Mac.
Qalculate! - Qalculate! is a multiplatform multi-purpose desktop calculator.
Calcbot for Apple Watch - Calculate, convert, and split tips from your wrist
NumWorks - The graphing calculator that makes learning math easier.
CALCU - CALCU is a simple, yet beautiful and powerful calculator.