This is an insert for Blokus. It consist of four containers for the pieces. The gameboard is placed upside down in the box and each container is attached to the gameboard to hold it in place.
There are several versions of the game. This was designed for the Mattel 81983 version. This is the Scandinavian version. The inner box is 325 mm and the board is 307 mm.
Here you'll find a laser cut version.