Unruly
<p>
Colour every square either black or white, in such a way that:
<ul><li>no three consecutive squares, horizontally or vertically, are
the same colour
<li>each row and column contains the same number of black and white
squares.</ul>
<p>
Left-click in an empty square to turn it black, or right-click to turn
it white. Click again in an already-filled square to cycle it between
black and white and empty; middle-click to reset any square to empty.