https://en.wikipedia.org/wiki/Hendecahedron

I was inspired by walter on Thingiverse: https://www.thingiverse.com/thing:784951 

I did however build this model from scratch based on the Wiki information, and I designed magnet sockets that minimize overhang related quality issues.

I'll let you refer to the wiki link for nerdy details, but basically a small pile of these polyhedrons is fun to arrange. They make a good fidget toy with, I don't know, some spatial and geometric learning benefit? I'm not a psychologist. 

Print as many as you like or have magnets for. I've discovered some fun assemblies that utilize 24 pieces. 8 was a fun starting point.

5mm Magnets Required

5mm spherical magnets should be inserted in sockets on each of the 11 faces. They should be snapped in after the print is complete. I just press them in against a tabletop. This model is specifically built for 5mm spherical magnets and the tolerances are not forgiving. Sorry I don't have a link to sources to purchase magnets. Evidently enough kids ingested such magnets that they are now difficult to find on major online retail sites. Shop hard.

The tolerances on the magnet sockets are subject to variation depending on print materials, print environment, the magnets you source, etc. Don't be surprised if you need to tune your settings or scale the objects. I've included a test block with a top, bottom, and side sockets to assist in such tuning.

The main .3MF file is a slice with 8 units, printed by object, in 4 colors utilizing the Bambu AMS. The .step file is a single unit.

The reason for spherical magnets as opposed to other shapes is that free rotation of the magnets is required for them to reorient themselves according to the polarity of an adjacent magnet. Without free rotation, magnets may repel, pushing your pieces apart. 

The intention of the octahedron socket cutouts is to ensure clearances in the socket for the magnet's rotation. They are designed and oriented to eliminate bridges and overhangs that may affect clearance. Most effective is if opposite corners of the socket are aligned vertically or horizontally only, therefore it's advised to print with the square “bottom” face down as provided.

I intend to publish models with additional socket sizes, so comment if you are trying to make this work with other magnets sizes. Additionally plan to add version sans sockets, and also a model of the octahedron socket cutout. 

Happy to direct anyone interested to these models in Onshape if they want to build their own scaled to their own spec, or use the socket for anything they like.