I have an Olivetti Lettera 22 typewriter and it's the perfect machine, just immaculately designed. But one thing that absolutely floors me and I have no idea how they did it - is they have infinite, programmable tab stops on a completely manual machine (no electricity). So you can set as many tab stops as you want, and then hit the tab key and it will jump between all of the stops in order. It's great for creating lists of things or for creating simple tables. How the machine is able to remember your settings, and allow you to jump between and clear you tab stops completely mechanically is just so cool to me and seems like a marvel of engineering.