How many calculators are on your Mac? For most, it’s the calculator Apple supplies in Mac OS X (or, OS X as it’s officially known in OS X Mountain Lion).
One calculator is never enough.
If you’re a Mac user who loves to calculate, and need more than Apple gives us for free, there’s the free RPN Scientific Calculator.
Handy Calculator will cost you a few bucks, but does more to justify the price tag. Copy results with a click on the display. Buttons are nominal but calculation capability is extensive, and even includes keyboard hotkeys. It’s also a big calculator and can float transparently above apps on the screen.
The same price gets Calculator Expert which mimics the iPhone’s calculator except in size (it’s huge), and comes with an editable history.
Similarly priced, but seriously geeky is the Console Calculator with the fewest number of calculator buttons ever.
No buttons? Just type in all your scientific functions for instant results. Personally, if I have to pay for a calculator I want buttons. The option to use a simple console interface (think Terminal app on your Mac) is nice, and may be faster for keyboard kings.