Bulls and Cows is a logic game that may be centuries old. In this solitaire version of the game, you attempt to guess the number the computer has chosen with a series of responses to your previous guesses. A kind of numerical Mastermind, the program will tell you which digits in your guess are in the number, and which are in the right spot.
Though the game has simple rules, it can be quite challenging. A high score function is built into the game. Before playing, I highly suggest you read "How to Play" in the Help menu, also accessable by pressing F1.