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.
Obsidian. I know it's not open source, but it just felt right.
Yep just swapped over from a self hosted solution with gitlab and sublime.. But that was to restrictive and the overall experience wasnt really good...
I then found a post somewhere on lemmy a post abotu PKMS and what people are using... One was obsidian... So I tried it and I'm really happy
Edit: I saw some comments about some missing self hosting. Since the notes are saved as standard md files you easily ca sync them with whatever you want... I set it up with my synology NAS and DS Drive, but any tool which can sync two-ways should be fine