Nine Men's Morris along with other similar games like Mancala, checkers, chess are all great games that can be played at the park or out in the yard with some chalk and some stones.
Nine Men's Morris directions:
The game of Nine Men’s’ Morris is played on a board, like above, with 9 pieces in one color and nine pieces in another color.
The object of Nine Men’s Morris is to make "mills" - vertical or horizontal lines of three in a row. Every time this is achieved, an opponent's piece is removed, the overall objective is to reduce the number of opponent's pieces to less than three or to render the opponent unable to play. Begin with the board is empty.
Player's toss a coin to decide who goes first. To begin with, players take turns to play a piece of their own color on any unoccupied point until all eighteen pieces have been played. After that, play continues alternately but each turn consists of a player moving one piece along a line to an adjacent point.
During both of these phases, whenever a player achieves a mill, that player immediately removes from the board one piece belonging to the opponent that does not form part of a mill. If all the opponents’ pieces form mills then an exception is made and the player is allowed to remove any piece. It is only upon the formation of a mill that a piece is captured but a player will often break a mill by moving a piece out of it and then, in a subsequent turn, play the piece back again, thus forming a new mill and capturing another piece.
Captured pieces are never replayed onto the board and remain captured for the remainder of the game. The game is finished when a player loses either by being reduced to two pieces or by being unable to move.