Providing an alternative to Windows’ desktop calculator, rpCalc delivers a lightweight RPN calculator that can be used for carrying out simple to complex operations. 

Just like most Hewlett-Packard calculators, rpCalc uses reverse polish notation (in short, RPN). All the four registers the calculator uses are displayed in the main window, while numbers are entered before the operations.

The calculator’s appearance is exactly the same on all devices. Just like a physical calculator, it displays all these buttons with numbers and functions that can be applied with the click of a mouse.

Buttons can be, of course, pushed or tapped, but rpCalc can be operated much easier by using the keyboard to type in numbers, operators or the text of the command (not case-sensitive). What is more, the “Tab” key can be used to automatically complete a partially typed command. For instance, typing in “pi” will display the value of the well-known constant in the main window.

A few commands have rather unusual labels so as to allow you to type them in: "RCIP" is 1/X, "tn X" is 10^X, "x<>y" is exchange, "<-" is backspace, "CLR" clears the registers.

RpCalc stores a limited number of recent calculations in the app’s History View, which you can toggle via the “OPT” menu. There is also the Memory View, which reveals the contents of the application’s memory registers.

You can configure RpCalc to remember the window’s position and size. The “Settings” menu allows you to modify the angle unit and the notation type, as well as a few other options, such as the number of decimal places, the maximum history entries or the auxiliary view scale ratio.

RpCalc is not just an alternative to the Windows embedded calculator, but also a virtual replacement for a physical HP calculator. Released under an open-source license, it can be used to perform various operations that also include trigonometrical functions, logarithms, square roots, exponentiation, and more.