There are several attempts at re-creating Luhmann's Zettelkasten in electronic form. The most important of these are:
Daniel Luedecke's Zettelkasten (http://zettelkasten.danielluedecke.de/), which is billed as being modelled after Luhmann's index card system,
Markus Krajewski's Synapsen (http://www.verzetteln.de/synapsen/), described as a "hypertextual" version of the slip box,
IdeaNotes (http://www.ideanotes.de/cms/), which is also claimed to be based on Luhmann's index card system, and
Eduardo Mauro's ConnectedText (http://www.connectedtext.com/), which makes no such claims, but which is to my mind the best of all of them.
They are all excellent programs, and while all but one of them are modelled on Luhmann's Zettelkasten, none of them tries faithfully to reproduce the system. This is not necessarily bad. It may be a good thing, because a too close adherence to a paper-metaphor, might be limiting and stand in the way of improvement. In fact, that's what I think; and I prefer ConnectedText in part because of it's remoteness from the paper-metaphor.
But this is not the main reason. The other three programs try to achieve the connection or linking between different topics or cards (mainly) by assigning keywords. But this is not what Luhmann's approach recommended. While he did have a register of keywords, this was certainly not the most important way of interconnecting his slips. He linked them by direct references (Verweisungen). Any slip could refer directly to the physical and unchanging location of any other slip. These systems establish connections only indirectly by assigning the same keyword to different slips, and especially in Daniel Luedecke's "Zettelkasten" there is no way to directly link two entries. ConnectedText with its wiki-links does connect two topics or entries directly (without the need for explicit numbers, as the database system takes care of that). It also allows keywords, of course.
Just as a experiment, I tried to reconstruct a electronic version of Luhmann's Zettelkasten that is more faithful to his idea. Here is what I came up with, using the commercial version of Notetab: Notetab Standard and Notetab Pro. Both have two features that allow one easily to recreate fairly easily a quite faithful electronic version of Luhmann's Zettelkasten. They are:
1. the Outline Feature, and
1. the Ability to create Hyperlinks.
An outline file (otl) in Notetab is simply a document that is "composed of two parts: the Headings list (or table of contents) on the left and the Contents editor window on the right. When you select a heading, its content is displayed in the editor window" (quoted from its Help File). Such a document can have 5.400 outline entries.
These different outline items can of course be numbered in accordance with Luhmann's numbering scheme.
It is also easy to link these outline items by hyper links. You simply need to enclose the name of an entry in square brackets. Double-clicking and holding down the crtl-key will then take you to the linked entry. Creating new links is just as easy. You type the number of the new entry, like "32/5a", select it and type Ctrl-Shift-B. Voila, the new entry is created, placed in the proper place of the outline, and open for editing.
To create references to other entries is easy. Just type the number and enclose it in square brackets. You can even have the links show up in red, if you want (available in Notetab Pro only).
In some sense, this reproduces Luhmann's setup too faithfully, as the inward growth will unduly separate two such notes as 1/1 and 1/2 by such slips as 1/1a, 1/1b1, 1/1c5, something that Luhmann himself found disturbing, at least to some extent.
But perhaps this not really as big a problem as it first appears, because the need for such continuations as 1, 1/1, 1/2, etc. is actually non-existent in Note-tab. Every outline entry can hold much more information than the octave-sized slips in Luhmann's system. So each numbered entry can contain just as much information as several separate slips in Luhmann's system. This also means that the limit of 5.400 entries - Luhmann accumulated 20.000 slips - is not as limiting as it might at first appear. If there was an average of a sequence of 10 slips per number, he would have accumulated only the equivalent of 2000 entries in Notetab. In any case, since it is possible to interlink Notetab files, even this is not a serious problem.
2GB of text storage (the theoretical limit of Notetab) should be enough for a life time of text.
Since it is possible to link in Notetab to different parts of an outline item (both internally within the same item and from other items), the length of an entry is not a real problem either.
It's also easy to assign keywords to each entry (and to use the keywords as a way of finding information), though direct links are designed the primary means of navigation.
The Notetab-Zettelkasten has several major advantages over the paper-implementation:
1. It is much more difficult to misplace slips
1. It has a powerful search function
What you have here is in many ways as close to a plain-text-wiki as you get in Windows. That all the information the information is stored in plain text should also be appealing to some.
While I have no intention of using it for my information, I believe it gives you a better idea of how work with the "sorcerer's assistant" (