Mastermind, written in Ruby, using Shoes.

Provides 4 difficulty levels (3 serious, 1 joke), each of which spawns a
new game of Mastermind with a random number. Within the GUI, we can
click on colors to select them, and then click on circles in the current
guess to make them the selected color. If we get the guess right, we
win; otherwise, the game shows us what merits our guess has. We repeat
until we run out of guesses or win.
