Mill game > the Nine Men Morris app for iPhone and iPad

TL;DR: just download and play instantly. This app has no ads nor any in-app-purchase. There is a brief instruction inside the game page.

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Nine Mens Morris is a strategy board game for two players that emerged from the Roman Empire. The game is also known as Nine Man Morris, Mill, Mills, The Mill Game, Merels, Merrills, Merelles, Marelles, Morelles and Ninepenny Marl in English

Game rules
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The board consists of a grid with twenty-four intersections or points. Each player has nine pieces, or "men". Players try to form mills— three of their own men lined horizontally or vertically—allowing a player to remove an opponents man from the game. A player wins by reducing the opponent to two pieces (where he could no longer form mills and thus be unable to win), or by leaving him without a legal move.

The game proceeds in three phases:

1. Placing men on vacant points
2. Moving men to adjacent points
3. (optional phase) Moving men to any vacant point when a player has been reduced to three men

Phase 1: Placing pieces
Nine Mens Morris starts on an empty board.
The game begins with an empty board. The players determine who plays first, then take turns placing their men one per play on empty points. If a player is able to place three of his pieces in a straight line, vertically or horizontally, he has formed a mill and may remove one of his opponents pieces from the board and the game. Any piece can be chosen for the removal, but a piece not in an opponents mill must be selected, if possible.

Phase 2: Moving pieces
Players continue to alternate moves, this time moving a man to an adjacent point. A piece may not "jump" another piece. Players continue to try to form mills and remove their opponents pieces in the same manner as in phase one. A player may "break" a mill by moving one of his pieces out of an existing mill, then moving the piece back to form the same mill a second time (or any number of times), each time removing one of his opponents men. The act of removing an opponents man is sometimes called "pounding" the opponent. When one player has been reduced to three men, phase three begins.

Phase 3: "Flying"
When a player is reduced to three pieces, there is no longer a limitation of moving to only adjacent points: The players men may "fly", "hop",[3][4] or "jump"[5] from any point to any vacant point.