There is no shortage of note-taking applications. Most will happily give you folders, tags, backlinks, a graph, and a small ceremony about building a second brain. I already have a brain. The problem is getting it to return to an earlier thought and do some more work.
A lot of writing about digital Zettelkasten treats Folgezettel as a historical accident, or says the addresses stopped mattering once software could link anything to anything. I disagree. The address records where a thought entered a line of development. Remove that and you may still have a useful notes application, but you have removed an important part of the method I want to preserve.
One permanent card is therefore one ordinary Markdown file with a meaningful address. Images, references, and indexes may help, but they don't get to become a second hidden truth. If the application disappears, the thinking must still be there.