It's been a long dry spell since I've designed anything here, but my kids are finally getting old enough to appreciate 3D printing. I've seen a lot of magnetic construction toys, but they all seem to involve either 1D (stick) or 2D (polygon) elements and they all have the problem where if you try to attach too many the magnets can't find a good way to stick and they start falling apart. With these 3D tetrahedral modules, the magnets are in the faces and free to rotate, so they will always stick.

Here's a video: https://www.youtube.com/watch?v=blHJbmeHJB4