Unfortunately, it is not a calculator I want to carry around with me (you would need really big pockets). Luckily there is a great free version of the HP48GX available for iOS: m48 This does so much more than 99% of the paid calculators available (not to mention nice extras like unit conversion, loan amortization, etc).
After spending some time rediscovering how to use the dang thing, I wanted to maximize my investment and use the equivalent on my desktop machine. Unfortunately, it doesn't look like there is much available, other than a paid version in the AppStore.
However, I was able to get the x48 0.6.4 emulator compiled for OSX. The only drawback is that it requires XQuartz/X11 to be installed (no longer default with Mountain Lion). I also bundled the app with Platypus which works great.
Here's a screenshot with an extra memory card installed (see the readme/docs for instructions).