The board
24 points on three nested squares, connected along their sides and by four spokes joining the midpoints of each square's sides.
Placing phase
Taking turns, each player places all 9 of their pieces on any empty point. Completing a mill — three of your pieces in a row along a line on the board — lets you immediately remove one of the opponent's pieces (their pieces already in a mill are safe unless that's all they have left).
Moving phase
Once both players have placed all 9, slide one piece along a line to an adjacent empty point each turn. Forming a mill (including by breaking one and re-forming it) removes an opponent piece the same way.
Flying
Once a player is down to exactly 3 pieces, they may move to any empty point instead of only an adjacent one.
Winning
You win if your opponent is reduced to fewer than 3 pieces, or if it's their turn and they have no legal move.