I did use the very first PCalc. I even wrote something that would translate a formula to PCalc's programming language. After switching to OSX, I never looked at it again, though. It may sound petty, but it was because of the price. I still think $10 is too much for a (fairly simple) calculator app.
Apple’s calculator that comes with OS X/Mac OS is simply terrible, at least in RPN mode to almost everyone who has used HP calculators.
Two that bite me all the time:
First, “2 Pi” on HP pushes 2 and Pi onto the stack, and the Pi is complete so if you then press “3” you end up with 2, Pi, and 3 on the stack and you are still in digit entry mode.
On Mac “2 Pi” first puts 2 on the stack, then overwrites that 2 with Pi, then when you hit 3 it overwrites Pi with 3.
If you do “2 ln Pi” on both HP and Mac you end up with ln(2) and Pi. On the Mac though if you then start entering a number it will overwrite Pi, whereas HP will lift the stack to make room for the new number.
Basically on HP the Pi key completes any in-progress number entry, pushes Pi, and enabled automatic stack lift so that you can start entering another number without needing to press ENTER. On Mac it lifts the stack if and only if pressing a digit would lift the stack, then overwrites the bottom of the stack with Pi, and leaves automatic stack lift off so that if you then start entering another number (or press Pi again) the Pi is overwritten.
Second, on HP memory recall behaves the same as Pi. On Mac memory recall overwrites whatever is on the bottom. For example suppose 7 is in memory. Then “1 MR” results in 7 on the stack. As with Pi it is still in input mode so “1 MR 5” results in 5 on the stack.
Unlike with Pi it does this even if automatic stack lift would be expected. “2 ln MR” results in 7 on the stack, with the 7 overwriting the ln(2). On HP it would result in ln(2) and 7 on the stack.
I used Mathpad for longer calculations, a bit of a niche application by Mark Widholm, which exists since System 7 or 8. It's a bit like Matlab, and also a bit like those apps where you write small steps and can track the computations (Soulver is one of those), but simpler and more direct than the former and much more capable than the latter.
For simple calculations, I used the standard calculator in "normal" mode. I've also always got one or two calculators on my desk (currently a NumWorks and an HP Prime). And since a few months, I also have Free42 on laptop and iPhone. If you like RPN, check it out: https://github.com/thomasokken/free42
