Nim

Nim is a game in which you have two or more piles (or containers) of objects (marbles, beans, whatever). The two players alternate moves, taking any amount of objects from only one pile, in any one move. The object of the game is to be the last player to take any objects. Try the game, with 1, 3, 5 objects in three piles:

A much simpler game is to have one pile of objects, and restrict the number that you can take. Let's say we start with 40 objects, and we can take from 1 to 6 objects in one move. Again, we win by taking the last objects.