Kinda like a 4-sided Dominoes! I think it's also been called 'Tetravex' and/or 'Travex' previously.

The object is to take all of the pieces from the right, and correctly place them on the left, so that all of the sides match. For example, if piece 'A' is above piece 'B', then the bottom number of A must match the top number of 'B', etc.