XCALC

XCALC application represents a highly configurable, “extended” calculator for 32-bit Windows that you can use for simple calculations using decimal or complex floating point, or hexadecimal, octal or binary integer numbers (32, 16 and 8 bit signed 2
The program uses RPN (Reverse Polish Notation), similar to the classic Hewlett-Packard handhelds. You can choose from anything between a small window consisting of a single number display only (which you can float above other programs ) to a full-fledged big display with all colours, buttons, bells and whistles.
The user interface is designed for ease of use, and you can use the keyboard or mouse for all operations as you please. To find 123+456, for example, key in "123 456 +". The weakness with using the keyboard is of course the lack of square root keys and such on the PC, but the keyboard interface is definitely faster than the mouse.
If you cant remember the keys for the various mathematical operations, you can always use the mouse and keyboard display for those, or press Alt-K or Ctrl-F1 to get instant keyboard help. You will also find memory store/recall functions, interaction with the clipboard, setting of various modes such as Decimal/Complex/Hex/Octal/Binary, and "Fix" or "Float" decimal settings.
XCALC will remember its settings and content between sessions; in the files XCALC.INI and XCALC.DAT are kept the various configurable items, the stack and memory registers, and also the screen position.