This little cube can be used to build structures out of cubes by joining them together with rods. Its great for building Burr puzzles or interlocking cube puzzles.
The set I've made has 15 mm cubes with 4 mm diameter rods. I used some fibreglass rod I had, but dowel or even kebab sticks should work. Printer filament could also be used. The cube size and hole diameter can be adjusted in the open scad file. Do a test print with a single cube first to check hole size against rod size. A tight fit is better. The holes printed vertically are generally smaller on my printer than the horizontal holes.
Once you have the hole size correct print multiples at once then start building.
The puzzle shown here is Staple Cubes by Oskar van Deventer.
Check out the Puzzle Will be Played site for many more puzzles you can build with these cubes.
Other things to build include polycubes, or minecraft stuff?