The Myst Chimney Game
After scrambling the colors, click away until they're all blue again.
Now try it for an 8 x 7 board.
Turns out 8 x 8 is easy ... but 8 x 7 is hard. Why?
Source Code
A simplified version of the idea behind
this web application can be seen
here.
This game is actually called "Lights Out";
you can read about the math
at
Jaapsch's puzzle site. I first saw in inside
a chimney within one of the Myst games.