Zim's markup, as I observed before, is remarkably close to that of ConnectedText. What I did not not before is that it accepts ConnectedText's URLs without any problem. Something like "ct://Personal/Zim%20Files" works right out of the box. Zim does not have categories, but it does have tags.
Some people believe (or at least suggest) that you have to make a choice between ConnectedText and Zim. I am not sure that this is the right approach. In fact, I believe that they may well complement each other. My main reason for this approach is the following:
ConnectedText does pretty much all I want. Its only weakness, as far as I am concerned, is that you cannot edit the same file(s) from different computers in DropBox. I understand why this is so. ConnectedText keeps its topics in a database that would be corrupted, if this were allowed. Accordingly, I just back up my files to DropBox when I leave home (with Syncback SE), restore them at work, and then do the same when I leave the office, i.e. Back up the office files to Dropbox and restore them at home.In any case, I will give this a try and use ConnectedText and Zim side by side for a while. Zim is like a little brother or sister of ConnectedText.
The only problem is that I sometimes forget to do this—and lately I forget it more often than I used to. I have, in the past, devised a variety of ways of using substitute applications or workarounds for allowing me to import or paste updated or new topics into ConnectedText when I have forgotten to back up. See here, for instance. Zim can fulfill this need as well. Having an application at home and at work, I can modify the text files at either place without worrying about corruption issues. I can also create references to ConnectedText, and I can store textual information in it that will never make it into ConnectedText.
In ConnectedText, I have created a topic called ""Zim files" that contains just this line: "[[$FILE:C:\Users\Manfred\Dropbox\*\Notes\*.*]]. It lists all the files created by Zim that I might need in ConnectedText. Since Zim saves its files in UTF-8, I could import them directly into ConnectedText, but that would mean the the header would also be imported. It's something like this: "Content-Type: text/x-zim-wiki Wiki-Format: zim 0.4 Creation-Date: 2015-04-05T15:06:57-04:00". It would not be a big deal, but it might be easier to open the text file manually from the Zim Files page and paste the contents of the files where I want to use them in ConnectedText.
Perhaps I should also mention that you could install Zim on the Mac, but it takes some doing and I have not tried it. See this page.