This is a collection of challenging puzzle games. Some are easier than others, but all can be difficult.

Nim (formerly The Rock Game)
Coin Swap
Dog's Crossing the River
Knight's Tour
Gentle Bishops

Nim has 3 different board sizes and the difficulty level of computer play can be adjusted. At any difficulty level, the computer will get smarter with every loss it takes. Challenge yourself to find patterns to win at the highest difficulty.

Knight's Tour has 4 different board sizes, 5x5 up to 8x8. The larger the board, the more possible outcomes and thus the more of a challenge.