I spent hours playing mastermind as a kid and this modern day re-incarnation is a really nice twist on the theme.<p>Mastermind was a nice primer for Sudoku, and probably those that are good at solving Sudoku are good at solving problems involving constraints in general.
Looks like a web implementation of the old People's Computer Company game "Bagels" published in the classic
<i>What to Do After You Hit Return: PCC's First Book of Computer Games</i>, now long out of print. PCC materials were published under a "free to use with attribution" copyright license, an really early version of the Creative Commons idea. I am not sure about the original source of the game, but I am pretty sure the use of "pico" and "fermi" was due to Bob Albrecht.