Very old game, this set made by J. A. Storer, 1995.
(12.5 by 12.5 by 1/4 inch wood board, 6.75 by 2.25 by 1.5 inch wood box,
1.25 inch white and red poker chips, and a 2.75 inch Chess king;
back of board is a Nine Men's Morris board)

These are the rules described in Murray's History of Board Games:

Pieces: A white King, 8 white pieces, and 16 black pieces.

Board and start position: A 9 by 9 board where the starting position, has the king on the central square, called the Konakis, with eight white pieces surrounding him, and a total of 16 black pieces at the edges:
Play: Players move alternately; white moves first. Only the king may move onto the Konakis.

Move: A move consists of moving a piece any number of (unoccupied) squares in the vertical or horizontal direction (i.e., like a rook in Chess).

Capture: A piece is captured and removed from the board when the opponent moves so as to occupy the two adjacent squares in either the horizontal or vertical direction (it is possible to capture up to three pieces on one move. Note that it is the act of moving that causes the capture; a piece may move safely between two opponent pieces.

Win: White wins if the King moves to any square on board perimeter. Black wins if the king is surrounded by black on all four adjacent squares, or on three adjacent squares and the Konakis.

Further Reading
Ludoteka Page, from:
Wikipedia Page, from:
Viking Age Page, from:
Stmoroky Page, from:
Passagen Page, from:
Scandinavica Page, from: