Genius is an unofficial Mastermind clone. Mastermine was originally coined by Mordecai Meirowitz. It involves trying to guess a four-digit password composed of six (or more... or less) characters (or colors, in the original game). The game is selling for $0.99 until 15 June, at which time it will stay at $4.99 until furthur notice.
Mac OS X 10.5 or later