This is a new silicone Castlemolds mold made by Hirstarts, Mold #220 Wooden Plank Mold.
Used to make wooden floors, cottages, stairs, bridges, doors, tables and almost any wooden objects you can think of.
Mold is approximately 5.5" x4.5", 14cm x 10.5cm.
Mold is designed to work with 25-30mm scaled figures. However, they can work for different scales depending on how you use them. For 16mm figures, use the windows as doorways instead. For larger scales, the blocks could be used as small bricks in a large wall.
You may notice a white residue on the mold, this is corn starch/baby powder. This is to stop the molds sticking to each other.