minesweeper
When I wasn’t addicted to Freecell, I was on to Microsoft’s Minesweeper.
I developed a pretty good strategy, and I started to wonder what proportion of games it is possible to win. So I wrote a program to play the game automatically. Of course, you need to implement the game first.
I implemented the game, and most of the auto-play logic. It worked pretty well, and you could play manually but ask for hints from the auto-play.
If anyone really wants to know, I could resurrent the source code and share it with you.