A web-based MasterMind - A free web-based RDBMS-backed version of the famous MasterMind game where the goal is to find the right combination of objects.
Ben's Marvelous Mastermind
Classic Mastermind Experience - stick round pegs in round holes. Sexy little javascript allows two to six colours in play.
Kin Lum's Master Mind - a classical, long time favorite game. Suitable for children to adult.
Master Mind - Classic Mastermind with a twist. Five Peg MasterMind: A java applet by Chris Russo.
Mastermind - Play Mastermind online against your computer.
MasterMind [german] - German version of a MasterMind game - guess 5 numbers from 1 to 7 (multiples allowed).
MasterWeb - An old "game of logic" brought to the Web.
Shockwave Mastermind
WebMeninges - Master Mind like game