Windows Reverse Polish Notation (WRPN) is a public domain calculator for Microsoft Windows that is modeled after the Hewlett-Packard HP-16c. This is not a Hewlett-Packard product.
WRPN uses Reverse Polish Notation, which uses the ENTER key instead of the "=" (equals) key.
In addition to all the functions you'd expect from an ordinary calculator, WRPN also has many features specifically designed for the computer professional:
Visit the dedicated website for WRPN at http://www.wrpn.emmet-gray.com