Currently I’m using Joplin with Syncthing-backed file system synchronization. I’m pretty pleased with it, as I do like tagging- and Markdown-based systems.
I plan to upgrade to server-based synchronization, but before doing that, however, I wanted to see what other people are using.
Edit: So far I see a slight favor towards Joplin and Logseq, but I totally didn’t expect (and appreciate) getting so many different answers.
I’ve been running the Joplin server for over a year with clients on four laptops and three phones and share notes with my wife and its wonderful. There are certainly quirks and sometimes sync issues but by and large I’m really happy with it. There seems to be one cluster of notes I have that always irritates a fresh client sync and it shows up at 50 conflicts but I work through it. Also my notebooks are huge and the first sync can take an hour. It’s a lot slower than I’d expect.
I’ve been running Joplin server for about two years now, and I concur. It’s been great.