For those who don't know what "zettelkasten" is: it is a way to organize knowledge on the paper cards, without any computers.<p>On the computer, there are a ton of note-taking / note-keeping programs, all of them support search, and many of them support hyperlinks. On the paper, there is no search (unless one manually maintains index) and hyperlinks require careful, manually organized card numbering system. "zettelkasten" is all about proper organization of those cards.