The calc2 program from page 144 of my yellowed copy of The AWK Programming Language is all I have needed for 98% of the calculations I make. If I need a spreadsheet, I'll use one, but specifying the RPN on the command line and getting the answer right there is the most convenient. Nothing else to load and unload, just type a command and get an answer. It even supports named variables! I save it as rpn.awk on the *nix or Windows systems I spend any time on. I spent about 10 minutes adding percentage and modulus operators, sometime in the last 17 years or so. It works!