CalcMadeEasy - Multipurpose Calculator is a very complete calculator app. If we compare it to the default calculator that ships with Mac, it blows it out of the water, but it also comes with tons of extra features that make your life a whole lot easier if you deal with numbers on a regular basis. It can be used for scientific and mathematical calculations, financial calculations, unit conversions and there is also a notepad that you can use to take notes and store them.
The calculator looks great. It is divided into three different panes, and it has a green display where the numbers you input and the results are shown. The panes are "Scientific", "Memory" and "Basic". You can use the mouse to press any of the available buttons or simply use the keyboard. The speed at which your input is detected is very good. I mention this because I have tried some calculator apps that were really slow and, thus, slowed me down.
I like that there is a drop-down menu with universal constants, like Pi, Golden Ratio, the number e, etc.
The financial calculator comes in handy if you calculate loans, payment rates and the like.
In short, CalcMadeEasy is a great calculator replacement app that comes with tons of extra features that can save lots and lots of time.