Mikulas Calculator

Mikulas Calculator is a simple program for mathematical calculations. The download page is here.
Note: it requires Java

Launch mikulas-gui.exe or mikulas-gui.jar (on linux) it and write an expression:

mikgui

It's possible to write an expression like 1 + 2 or sin(pi) to calculate. You can also use a predefined function or a constant, press ctr+space and choose one:
proposals

It's possible to use a predefined function like sqrt and define a custom function like pyth.
Expressions are lines without : and just these are expressed in the Result part, like pyth(3, 4):

mikgui

There is also a text console version, you can write the same using mik:

mikgui