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.
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.