Calccis

Calccis is a reverse polish notation (RPN) calculator.
It supports basic arithmetic, trigonometrical, logarithm and exponent calculations for real and complex numbers. Both degrees and radians can be used for trigonometrical functions. There is an undo stack, which supports undoing and redoing the 100 latest operations.
Calccis does not copy or mimic any existing physical calculators. However, the operation of the stack has been influenced by how the stack works in the 1990s Hewlett-Packard HP-48 family of calculators.