The Royal Game of Ur
I was studying some ancient history and came upon the Royal Game of Ur, as it was called. The British museum (I believe it was) gave some rules of play that didn't make much sense to me, and I began thinking of how I'd do the game-play. This is the result. My mom plays this almost every day.
Star Trek 3D Chess
The bullies in High School used to mock me (or so they thought) by calling me "Mr. Spock" (about 1970), so recently I felt compelled to give a computer my understanding of the 3D chess game, as that character did in one episode of that TV show. Here again, the rules I found online didn't match what I would have implemented, so I did this my own way.
The Rasbold Maze
A good friend of mine bought his young son a Commodore 128 (back when they were just getting popular - 1986, if I recall), so I wrote a maze program for the kid. There weren't too many games around for that platform, and I suspected a 3D challenge would be better than the usual 2D games just coming out. Later in 2002 when I was on a team that was building a "smart phone", I quickly threw this together again so the platform (which I helped design) would have at least one game. Unfortunately our parent company saw no need for such a phone, and the project was cancelled.