Nine Mens Morris
This ancient game has been called by many names such as Mills, Merels, and even Cowboy Checkers. Thousands of years old it was known in Europe, Africa and Asia, although now it can found being played all over the world....and online!
A two person strategy game it is fun for both children and adults.
Since it has been played for so long and in so many places there are different rule variations. So just make sure you and your opponent are playing by the same set of rules.