I don't know about other people, but for a calculator I still swear by my old HP48SX or my newer HP49G. Using RPN, of course... never seen anybody give up using that once he really digs it.

On the PC, I've been experimenting with all kinds or replacements, but they all had drawbacks. I've been trying to use HP emulators, which were difficult to use because of the funny keyboard mappings, plus you needed ROM images for them and that didn't always seem to work either. There are of course RPN calculators for Windows (and Linux, my other platform) out there, but I never found one that offered the flexibility I admired in the HP calculators. Most aren't programmable, to start with.

Today, out of the blue (I wasn't even looking for something like that), I found what seems like a fantastic solution: the C# Programmable Calculator. It's RPN, it has a lot of features out of the box, and it's very easily programmable in the language I'm using most these days: C#. Supposedly, I can even create graphics from the calculator, but I haven't tried that yet. Looks like a perfect solution for me, and it's Open Source, so go get it!

I guess it's difficult to extend it with an equation editor like the HP has, but then sometimes you lose :-)