Obsidian is pretty damn good.

Seems to not be FOSS 😔

Oh dang I thought the source code was public.

It seems to me like they attempt to appear that way, the have a lot of their docs and stuff on github and link to it from their main site, but the actual application code is not there

I have standard notes on a VPS and use it for everything

Yeah looks like they have a plugin API and a private codebase.

How does that handle offline work? I don't have cell service so I'd like to still be able to read and write offline and have it sync next time I'm on wifi (should have mentioned that in the requirements)

I've never had a problem. it always syncs changes to the server next time I have access. and you have a copy locally when you don't have service.

Doesn't do any of the last bullet point but Zim works well for this, usable on Android w markor. Turtl also worth a look

Hey, I might be able to help you here. I write all my notes in markdown, so it stays readable on any device and platform. On Linux and Windows there is VNote which is open-source https://github.com/vnotex/vnote. On Android - also open source - you can use Markor. Very simple and effective for small touch devices (I have even used it on E-Readers). VNote has the advantage of opening a large amount of tabs from multiple notebooks, on multiple workspaces, all helping you stay organized. It also holds advanced features such as regex-search. Over time, I also customized it with keyboard shortcuts for global search and tab navigation so it feels more like a browser. It does some Markdown rendering while you type (text size, color), as well as it offers a built-in html viewer, applying latex formulas etc. all at the press of a button.

Yes Markor is awesome, I also have used Zim in the past.

I don't use note taking apps very much, but if you haven't chosen one yet, take a look on this one

Notesnook by Streetwriters LLC

Notesnook | Open source & zero knowledge private note taking app

Express yourself with freedom, no spying, no tracking — only private notes. Unlike Evernote and other note apps, your data is private — not ope...