kidsmath

Kidsmath is a simple and easy-to-use calculator that allows you to perform simple calculations. The application has an intuitive user interface that has been exclusively designed for kids to make simple calculations, like additions, subtractions, multiplications, and divisions.

It can also calculate square roots and percentages. It even includes the PI number to make geometric calculations. What basically distinguishes it from the one included with Windows is that this app can make calculations in different numerical systems like decimal, hexadecimal, ASCII, and binary. The numbers on the calculator are of a big size, but those that you type on the screen to perform calculations are too small. What is great is that the calculator can be used with the mouse or even with the keyboard.
In short, if the intention is to have a simple calculator for everyday life, I would use the one included with Windows. However, if you like or need a calculator that includes many numerical systems, this one will suit you.