WHile wandering around r/pkms I found someone discussing using SilverBullet, a free "Programmable, Private, Browser-based, Open Source, Self Hosted, Personal Knowledge Management Platform" that's been in development for five years.

https://silverbullet.md/
https://github.com/silverbulletmd/silverbullet
https://fosstodon.org/@silverbulletmd

Intro & demo video from a year ago. (User page contains numerous SilverBullet videos.)

https://www.youtube.com/watch?v=mik1EbTshX4

It's a system you run locally inside a web browser. In the browser lives a Markdown editor with live preview as you type, a la Typora or Obsidian (which can be turned off if desired to provide inline Markdown).

You can navigate file-by-file via a meta glossary page, or via bi-directional links within pages. It has basic outlining capabilities, and folding, although no hoist or zoom -- it realistically is more a wiki than an outliner.

https://silverbullet.md/Outlines

Simple tasks with checkboxes.

https://silverbullet.md/Task

Simple database tables created using tagging, frontmatter attributes, and bidirectional links. You can query tables, tasks, tags, pages.