Nine Mens Morris
Also called Merrills or Muhle.
Equipment
The board consists of three nested squares connected by a line through each of the four sides. Pieces are placed at the corners of the squares and the intersections on the sides. Nine pieces are needed for each player, for a total of eighteen pieces. Beads, coins, checkers, and colored glass "stones" all work well.
Print out a board:
Object
The key concept of the game is the mill: a straight line of three pieces of the same color along a line on the board. When a player forms a mill, that player can remove any one of their opponent's pieces that is not also part of a mill. If all of the opponent's pieces are in mills, then any piece may be removed.
There are two ways to win Nine Mens Morris: Reduce the number of your opponent's pieces to two, or block all of your opponent's pieces so they cannot move.
Gameplay
The game begins with an empty board. Randomly select a player to go first. Gameplay proceeds in three phases. If a player forms a mill during any of the phases, that player immediately removes one piece belonging to their opponent.
In the opening phase, the players alternate placing pieces on the board. Once all pieces have been placed, then the players alternate moving one of their pieces into an adjacent, unoccupied space. Pieces must move along a line on the board, and may never jump another piece. The ending phase begins when one player has been reduced to only three pieces. At that point, the player with three pieces may jump a piece to any position on the board.
The game ends when the the winner reduces his opponent to two pieces (thus can no longer form mills), or blocks all of his opponents pieces from movement.
Strategy
There are three types of spaces on the board: corners, sides, and intersections. Mobility is key in Nine Mens Morris--a single piece trapped by opposing pieces is useless. Therefore, corners are weak since they only have two adjacent spaces (it's easy to get a piece trapped in a corner). Sides are stronger than corners, but weaker than intersections, since they have three adjacent spaces. Intersections are the strongest positions on the board since they have four adjacent spaces.
Opening Strategy
The first player enjoys a slight advantage: he can always claim two intersections. If the second player isn't careful, a strong first player has a good chance of claiming three of the four intersections. The second player (red) should not be too hasty in claiming the last intersection, if the board looks like this:
If the red player takes the last intersection, then the blue player will lay a common trap by playing in the corner between his two intersections, creating two potential mills. Since the red player can only block one of them, the blue player will succeed in getting a mill and red will lose a piece!
Be very careful not to lose any pieces in the opening phase! Being even one piece short can be disasterous at the start of the second phase.
In the opening phase of the game, it is often better to attempt to separate the opponent's pieces from each other and block them from moving than to form mills. But be warned: a crowded board with few free pieces is very delicate. One wrong move can easily shift the advantage to your opponent.
It is not good to continually force your opponent to block you from creating mills in the opening phase. This will likely lead to all of your pieces being blocked and puts you in a weak position for the midgame.
Common Formations
In this diagram, blue has a very powerful arrangement of pieces called a double mill. It allows a player to complete a mill on every turn by moving one piece back and forth between two positions.
It is very difficult to counter a double mill. Ideally, a player could form a mill of their own and remove a piece from the double mill. However, it is hard to form a mill when you are losing pieces every turn. Another alternative is to try and block the piece from moving back and forth, but it is also unlikely that the double mill player will let you get away with it. Sometimes it is possible to threaten to form a mill that requires your opponent to break up his double mill to block. Of course, the best defense against a double mill is to keep your eye out for them and never let your opponent form one in the first place.
Variations
Five Men's Morris
A smaller, quicker game than Nine Mens Morris, this game uses only two rings of the Morris board. Each player has five pieces, and gameplay works exactly like Nine Mens Morris.
Note that on this board, a mill can only be formed along the sides, not radiating out from the middle like on the larger board.
Eleven Men's Morris
Uses a board with three concentric squares, but with lines connecting the corners, allowing mills to be formed diagonally. Each player has eleven pieces, and gameplay works exactly like Nine Mens Morris.
Twelve Men's Morris
Uses the same board as Eleven Mens Morris, but each player has twelve pieces. There are twenty-four positions on the board, so if both players play a perfect opening phase (no mills were formed), the game will end in a draw.