Interesting you ask.... Emacs Calc was inspired by the HP-28.

https://www.gnu.org/software/emacs/manual/html_mono/calc.htm...

It's not the same, but having used both, they are very similar in overall feel.

> Are calc and emacs missing something that made HP great?

A couple things:

First, having specific hardware is (was?) a nice thing.

Secondly, the HP28/48 programming model was very, very orthogonal. It was a more impoverished Lisp than even elisp is today, but it pervaded the entire software stack. While people referred to 'RPL' and 'System RPL' with two different names, the truth is that there was no real distinction between the programming language you used as a user and the programming language used by HP to build the machine in the first place. This kind of solidity and general 'gestalt' pervaded the operation of the machine and made them joys to use.

You can try an HP48 here: http://www.poleyland.com/hp48/index.html

dc on the unix command line (linux too), is an rpn calculator. I use its non rpn counterpart bc. I've been told they aren't great (buggy), but for simple math they work fine.

I used a hp 32S in college, less mistakes make with rpn then entering calculations the other way. though newer calculator allow entering of whole equations ((10 *5)^2)/3 made this less useful.

The hand helds are more portable than emacs.

Single hand operation and wonderful click feel of HP calc buttons (before the 49 model of course) ;)