SpeedCrunch is the super-fast and keyboard friendly calculator, which support extended expressions. It contains the built-in library of math constants, variables, and equations for all calculations. It is available for Windows, MacOS and Linux platform and comes up in a number of languages.
It is a scientific calculator featuring a keyboard-driven user interface that displays the results as you enter. The software comes with more than 80 built-in mathematical functions, where you may define your own functions too.