C_011 - As for 3D printers, I think a great use for them would be to print modular marble runs, made of plastic or iron. If the run is for iron marbles, magnets can also be used to create even more unique runs. Ideally, they would be compatible with certain types of modular blocks, such as large children's blocks, so that those blocks could also be used to build the marble run. It would also be great to organize tournaments with these runs so anyone can participate and compete.