I have written this applet as an exercise, please see http://www.puzzles.com/PuzzleClub/WindmillPuzzle/WindmillPuzzle.htm for Oskar's original
Instructions
When the arms of the Windmill rotate gravity moves the balls in the top arm
downwards. The first ball goes down the left side and the second down the right
etc.
Your aim is to get all the balls lined up with the small coloured markers, by
a series of rotations.
There are 7 levels each more difficult.
Use right click to rotate clockwise, and left click to rotate anticlockwise. Or use the left and right arrow keys.
New button will shuffle the puzzle.