diff --git a/Model/Sources/Model/Board.swift b/Model/Sources/Model/Board.swift
index 3ade19a..6217766 100644
--- a/Model/Sources/Model/Board.swift
+++ b/Model/Sources/Model/Board.swift
@@ -42,15 +42,21 @@ public struct Board {
         }
     }
     
+    public func forEach(_ consumer: (Piece?) -> Void) {
+        for column in grid {
+            for piece in column {
+                consumer(piece)
+            }
+        }
+    }
+    
     public func countPieces(filter: (Piece) -> Bool = { piece in true }) -> Int {
         var count = 0
         
-        for column in grid {
-            for piece in column {
-                if let piece = piece {
-                    if filter(piece) {
-                        count += 1
-                    }
+        self.forEach {
+            if let piece = $0 {
+                if filter(piece) {
+                    count += 1
                 }
             }
         }
diff --git a/Model/Sources/Model/Rules/FourInARowRules.swift b/Model/Sources/Model/Rules/FourInARowRules.swift
index e9851ff..15d7305 100644
--- a/Model/Sources/Model/Rules/FourInARowRules.swift
+++ b/Model/Sources/Model/Rules/FourInARowRules.swift
@@ -32,14 +32,7 @@ public struct FourInARowRules: Rules {
     public func isValid(board: Board, move: Move) -> Bool {
         guard self.isValid(board: board) else { return false }
 
-        switch self.state {
-        case .Playing(let turn) where turn != move.player:
-            fallthrough
-        case .Finished(_):
-            return false
-        default:
-            break
-        }
+        guard case .Playing(let turn) = state, turn == move.player else { return false }
 
         if case .InsertOnSide(.Top, let offset) = move.action, offset >= 0 && offset < self.columns {
             return board.fallCoordinates(
diff --git a/Model/Sources/Model/Rules/TicTacToeRules.swift b/Model/Sources/Model/Rules/TicTacToeRules.swift
new file mode 100644
index 0000000..3d5a61e
--- /dev/null
+++ b/Model/Sources/Model/Rules/TicTacToeRules.swift
@@ -0,0 +1,82 @@
+public struct TicTacToeRules: Rules {
+    public var state: GameState = .Playing(turn: .A)
+    
+    public var history: [Move] = []
+    
+    private let columns: Int, rows: Int, minAligned: Int
+    
+    public init(columns: Int, rows: Int, minAligned: Int = 3) {
+        self.columns = columns
+        self.rows = rows
+        self.minAligned = minAligned
+    }
+    
+    public func createBoard() -> Board {
+        Board(columns: self.columns, rows: self.rows)!
+    }
+    
+    public func isValid(board: Board) -> Bool {
+        abs(board.countPieces(filter: { p in p.owner == .A }) -
+            board.countPieces(filter: { p in p.owner == .B })) <= 1
+    }
+    
+    public func isValid(board: Board, move: Move) -> Bool {
+        guard self.isValid(board: board) else { return false }
+        
+        guard case .Playing(let turn) = state, turn == move.player else { return false }
+        
+        if case .InsertAt(let coord) = move.action, board.isInBounds(coord) {
+            return true
+        }
+        
+        return false
+    }
+    
+    public func validMoves(board: Board) -> [Move] {
+        let player = Self.nextPlayer(board: board)
+        
+        return self.validMoves(board: board, for_player: player).map { Move(player: player, action: $0) }
+    }
+    
+    private static func nextPlayer(board: Board) -> Player {
+        if board.countPieces(filter: { p in p.owner == .A }) > board.countPieces(filter: { p in p.owner == .B }) {
+            .B
+        } else {
+            .A
+        }
+    }
+    
+    public func validMoves(board: Board, for_player player: Player) -> [Move.Action] {
+        var moves: [Move.Action] = []
+        
+        for col in 0..<board.columns {
+            for row in 0..<board.rows {
+                if board[col, row] == nil {
+                    moves.append(.InsertAt(where: Coords(col, row)))
+                }
+            }
+        }
+        
+        return moves
+    }
+    
+    public mutating func onMoveDone(move: Move, board: Board) {
+        self.history.append(move)
+        
+        guard case .InsertAt(let coords) = move.action else {
+            fatalError("Illegal move \(move.action)")
+        }
+        
+        if FourInARowRules.countMaxRow(center: coords, board: board) >= self.minAligned {
+            self.state = .Finished(winner: move.player)
+        } else if board.countPieces() == board.columns * board.rows {
+            self.state = .Finished(winner: nil)
+        } else {
+            let next: Player = switch move.player {
+            case .A: .B
+            case .B: .A
+            }
+            self.state = .Playing(turn: next)
+        }
+    }
+}