Magnetic Slider Puzzles

According to Wikipedia, sliding puzzles have been with us for a very long time. The classic 15 Puzzle shown above was "invented" by Noyes Palmer Chapman around 1874. Over the years there have been many variations on the original, with colored blocks, jumbled pictures, variously sized grids, etc.. I have fond memories of playing with the 15 Puzzle and some of the variants growing up.

These puzzles all follow the same pattern, a shallow box base holding a grid of flattened square blocks, with a single block missing. Adjoining blocks can be slid into the empty space leaving behind a new empty space. In this way blocks can be moved around the board (one at a time) to "solve" the puzzle by arranging the pieces in a particular pattern. A clever tongue and groove mechanism held the movable pieces firmly to the base, yet allowed them to slide freely into the empty space.

A quick search shows that there are many Things already that show you how to make various kinds of sliding puzzles. An