Dimension: 23 x 23 x 0.25cm

It is a Three, Six, Seven, and Nine Men's Morris set.

Nine Men's Morris is an ancient game played as far back as 1400 BCE and famous during the Roman Empire. It may be a precursor to Tic Tac Toe. The gameplay is similar to tic tac toe in that the player is trying to make rows of three, called a "mill" while preventing their opponent from making a mill.