I use Zim for this, backed by Dropbox. It's just text files, and Zim is just an editor, not a server or anything like that.
If I ever tire of keeping a personal wiki for whatever reason, all of the content I've built up in it will remain organized as files within directories.
Came here to say this. I've been using Zim for a little over 2 years, now, and it's become an every-day planning/journaling/notebook/project habit. Lightweight and doesn't get in your face with complexities or demands.
I highly recommend the 'Backlinks' plugin to improve the wiki functionality; leaves Roam standing in the dust for personal use.
+1 for Zim+Syncthing, been using it for almost 2 years now. The only gripe I might have is against the near useless search and proper support for code blocks.
If I ever tire of keeping a personal wiki for whatever reason, all of the content I've built up in it will remain organized as files within directories.