TheCalcMan is a free, small, no installation calculator replacement.
99% of users use calculators for doing simple calculations. And most use the Windows Calculator.
How to use it:
You first type the first number from the keyboard. Then you choose the operator using the mouse. Then again, you use the keyboard to enter the second number. It causes annoyance to move your hand from keyboard to mouse and keyboard again.
So I made TheCalcMan. It has a text box to enter the WHOLE expression(e.g., 2+3), and then you press enter. And you get your answer. Yes, it's that simple.
It combines the power of command-line apps and the usability of GUI apps.
It supports user-defined constants, which means that the user can set pi=3.1416 and do pi*8!!
It is a small app. Just 18 KB download. It enables you to define constants also. It has got visual effects too. Apart from the four operators, it supports Exponentiation and Factorial.
It supports constant operator(for doing 2+3+4+5+6+7 or 2*3*4*5*6 and like that).
No installation required. No dlls. Just unrar and go. And its a freeware. It requires .net framework 3.5, though.