IBM Selectric typewriters use swappable typeballs instead of hammers, allowing the typist to use any available typeface. With no-one manufacturing new ones, it's an obvious target for 3D printing: you could have any font you like! But typeballs were steel–even lead is too soft–and it's a problem to fabricate letterforms that are both sharp and durable enough for practical use. Problem solved! Sam Ettinger:
The blank typeball is based on 1944GPW's typeball on Thingiverse, which is released under a Creative Commons-Attribution license. I suspect that my project wouldn't exist if it weren't for this one. I had to change most of their typeball dimensions, and there are major issues with the way their characters are generated, but I sure as heck would have made those same errors myself, so I'm infinitely grateful for the people before me who documented their processes!
Another project that deserves a lot of credit is The Sincerity Machine by Jesse England. Jesse is a delight and a constant source of creative inspiration for me, and it brings me great joy to watch this project evolve with him.
Would there be any impediment these days to making new typeball machinery? Say, a USB ribbon printer that prints with a typeball.