XCALC is a highly configurable calculator that can be used for simple calculations using decimal or complex floating point, or hexadecimal, octal or binary integer numbers. 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 colors, buttons, bells and whistles.