Personal Wikis fit right in, if you ask me! I too tried out a wiki first (wiki.js) and it was really nice, but somehow obsidian felt "right" to me. No Web Browser to open, local files, offline access. It lowers the barriers a lot and I can quickly open it, write down a word I'd like to remember, and close it again. It is basically a wonderful PKMS but also my favourite quick note App.
Personal Knowledge Management Systems (PKMS)
A place for people to discuss Personal Knowledge Management Systems (PKMS) such as "Building a Second Brain" (BASB), Obsidian, and more.
That's one of the elements of Zim Wiki I really like, no browser, local files, offline access too. The downside being that there's no mobile version (so far as I'm aware), and there's some other limits, but for a desktop/laptop personal wiki, it's been great to me.
That said, thanks to Joplin being cross-platform, it sees more use on my end, which I imagine is similar for folks using Obsidian (alongside other formatting options it provides).
I wanted to learn TiddlyWiki but I wanted to be able to edit from my iOS device. As far as I remember, I needed an app to do that, one that wasn't officially supported. So I went to Obsidian instead. I appreciate that it stores notes on your device so you are not locked in in case anything happens. And that I have an officially supported iOS app.