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.
Trilium for the same reasons, but the featureset of Trilium is more like Obsidian.
Trillium was originally created to be an open source replacement for Roam Research. It’s similarities to Obsidian are purely coincidental, probably because Obsidian is designed to be a cross between Roam and Evernote.