They're the backend for Noteself, such I've been using for a few years now as my life organising note taking tool.

I have it setup self-hosted, and as long as I have internet I can connect to it and update it. Of I don't have internet I can browse the contents as per the most recently cached version.

(I can also save it to a single HTML file and back that up in numerous off site locations).

https://noteself.org/