Long ago, on Mac OS (6? or 7? I think) was a game called Triazzle. It was made by Berkley Systems (makers of those fun screen savers, AFTERDARK. Yes, I realize that these days screen savers are not necessary to prevent burn in, but they were fun, and still serve the purpose of having your computer screen saver come on after (a set time of) being idle; after-which you could opt for a password prompt to continue.
Triazzle puzzles are fun, and now they have announced that Spring 2009 it will be in the iTunes store for iPhone and iPod Touch. (yay!)