ColorCode is a free advanced MasterMind clone with lots of different game variants, from the very easy up to really challenging ones. You can combine any color count from 2-10 with any column count from 2-5 and allow or not pegs of the same color. Or you may select one of the 5 predefined levels of difficulty. ColorCode has also a rather intelligent ;-) built in MasterMind solver - so you can let the computer guess for you (nope, hes not cheating - really).
Enjoy!