From the developer: "Calculator.NET is an enhanced version of the standard calculator in Microsoft Windows. Calculator.NET uses RPN (Reverse Polish Notation), which is used by many pocket calculators, e.g. from HP. If you have used a HP 28/32/42/48, or any other RPN calculator, you will feel right at home. Some of the enhancements included are: RPN, more functions, and improved use interface. This program is completely free."