The board is 8x8 in size and every player has 4 playing pieces. Object of the game is to move 2 of the 4 pieces on the opposing side of the board.
The name of the game comes from the moving mechanism of the playing pieces: they can move 1 field in all 4 directions, but they are flipped over every time when they move (I guess they "flop" when moving to the left or right side).
All playing pieces are numbered from 1-4 on one side and from 5-8 on the other side. Since the pieces are always flipped over, the value of the pieces is changing with every move and it needs much thinking in advance to find the best moves.
Another problem is, that the pieces should always look in the same direction. To assure this, each piece has 2 dots on the front and 2 on the back, but when comparing the pieces on the game-box with the ones included with this game, it is obvious, that this designing problem is not solved very well.