German here - I misread the title as Zettelkästchen and thought that the word Zettelkasten was a clever way to work around the umlaut. Looks like I was wrong ;)

German here - I misread the title as Zettelkästchen and thought that the word Zettelkasten was a clever way to work around the umlaut. Looks like I was wrong ;) A Kästchen is a small Kasten (box) by the way.