It's the ubiquitous Tic Tac Toe game. I prefer to call it TTT.
I've included the source code for the application, with heavy use of commenting. I use a similar approach to the Hill Climbing algorithm, but I calculate it in a different way.
Originally, this was an assignment for AI class. I began implementing it in Java, but after a week I hadn't done anything significant. I completed a complete code rewrite (in Java) the night before the due date. The next day, I left the damn thing at home. In an hour and fifteen minutes DURING class, I completely recoded the program in C, paid someone for a spare floppy, and turned in the program listing hot off the laser printer at the end of class.
Despite the time constraint, I even found time to include detailed comments on the most important aspects of the code. The main function does not include very many comments, but it's not that important anyway.
Enjoy, or whatever you do to these things.
Source code included, builds in GCC and VC++.NET 2003
For included binary file: DOS emulator such as CMD.EXE