Rubik's Fifteen, the mechanical puzzle, came out around 1988 at the same time as Rubik's Clock. Both are terrific because the mechanisms are quite clever. However, both are kind of easy.
It may seem that Rubik's Fifteen is double sided. Yes and no. Yes, both sides have numbers. One side is red with Roman Numerals, the other side is yellow with regular numbers. The yellow side is harder than the red side because some numbers get hidden under the black frame.
I originally solved the yellow side by focusing on the red side where I could see all of the numbers, because a 7 on one side is still a 7 on the other.
Now you don't have to buy the actual puzzle because the virtual puzzle is here and it's free. But the virtual model is missing that tactile magic.