Over the years, I have written many posts on Luhmann and his Zettelkasten. Here is a search of the blog that combines them all.
As you all know, I have decided against a strict or faithful implementation of the Zettelkasten, but have opted for a hypertextual method as implemented on a personal wiki (ConnectedText). I do think, however, that it captures the spirit of Luhmann's system. In fact, I'd like to think that he would use a wiki-like solution as well, if he were alive today. There are other ways of doing this, of course. Daniel Luedecke's Zettelkasten uses mainly tags. I have written about it before, but it has changed a lot since I first wrote about it (see the link above; see also here). Eventually, I will have to write a full review.