Calcmadeeasy Free is the free version of a paid scientific calculator app ($2.99) for Mac OS X. Calcmadeeasy Free is designed to provide you with general math and scientific calculations, although there's not a great deal of true scientific functionality available in the free app compared to the full version.
Calcmadeeasy Free installs quickly and the interface is attractive. The screen is divided into two panes, one for scientific functions on the left and more traditional numeric and math functions on the right. A single line of output at the top completes the interface. The buttons are large and easy to hit, which is a nice feature. You can change the colors and appearances of the buttons through configuration options. There's also a built-in notepad accessory for copying calculations and other comments, which can be shared with others.
There's a plethora of calculator apps available for Mac OS X, some modeling physical calculators and employing their stack management techniques (such as HP's RPN), but Calcmadeeasy Free is a straight-forward calculator. For most people this will be fine, but if you're heavily into the sciences or financial calculations, the free version won't be enough.