Scientific/engineering firmware repurposing HP business calculators!
An HP RPN calculator with interval output
RPNCalc - The command line Reverse Polish Notation (RPN) Calculator
A suite of RPN calculators and a class library for Object Pascal
Simple Java computer algebra calculator
Simple RPN desktop calculator, implemented with wxWidgets and Lua.
Reor is a winsome calculator with loads of functions, by Ajay Menon.
a reverse Polish notation multi-precision pocket calculator software
A functional HP-style command-line RPN scientific calculator
RPN calculator running on Windows and Linux