I’ve been playing with a replacement calculator for the Mac. Magic Number has been out for a while, but is new to me. There is an incredible amount of functionality built into the calculator, yet it is incredibly easy to use.
To get a basic sense of Magic Number, spend a few minutes going through the Getting Started page. Note that a number of the screen shots are short little animations (start them by clicking the classic play triangle).
The thing I like the most about Magic Number is that the math looks like math. For example:
Even after you enter a calculation, you can edit individual elements and recalculate. This is the tiniest tip of the iceberg here. Magic Number is incredibly robust, chock full of features. And a new, free update is coming in mid-August, supposedly full of new stuff. Can’t wait.

I’d settle for something that was as relatively easy to read as iOS’s native calculator, Helvetica Neue notwithstanding.
Thanks for the heads up on this app.. very nice!
No RPN. Not for me.
Looks cool, but what I really need is capable calculator that lives in the menu bar, and can be activated globally with a hotkey. I’m still using Calq, but it’s no longer supported, and it’s capabilities are pretty limited. I found one called Numi in the MAS that’s much more capable, but it doesn’t play well with fullscreen apps.
http://web2.0calc.com/
this one’s free