Apps with 'Reverse Polish notation (RPN)' feature
PCalc is the powerful choice for scientists, engineers, students, programmers, or indeed anybody looking for a feature rich calculator.
Programmable Reverse Polish Notation (RPN) calculator that lets you create custom buttons.
galculator is a GTK 2 / GTK 3 based calculator with ordinary notation/reverse Polish notation (RPN), a formula entry mode, different number bases (DEC, HEX, OCT, BIN) and...
Excalibur for Windows 32-bit version is a freeware full featured RPN-only calculator. This is a serious calculator for serious users.