A puzzle where all the pieces are cubes of identical size. Each cube can be distinguished from all the others by simple colouring/pattern schemes.
Each cube has several small strong magnets inside it at various locations and orientations. The cube is made of a non-ferrous material, but there may also
be snaking threads of metal inside the cube to channel the magnetic fields in interesting ways.
This way, each cube has a different magnetic field structure on the outside. The puzzle is then to create various configurations of cubes that hold together magnetically.
This could take quite a bit of design and tuning to create cubes which had sufficiently bold and varying magnetic properties in such a way that a variety of interesting puzzles was available with a relatively manageable kit (say 27 blocks or something).
Interesting things are that although each cube has the same shape, their properties when connected together are very different, and when you add a cube to an arrangement, the effects can reach right through the arrangement, they wouldn't always be just confined to the neighbouring cube.