Selfhosted

It depends on the notes, for me:

I've had an oddly long-running obsession with Tiddlywiki!

It has a bit of a learning curve, but it's VERY flexible. My favorite part being that by default it's just a single, portable, HTML file. No special app required besides a browser, no accounts, and you can just sync it like any other file. (Syncthing, Nextcloud, and friends)

There's also an app called Tiddloid for Android to make managing and saving a little easier, but they open in any browser.

I have a Tiddlywiki that I use like one might use Obsidian, where I just stash stuff I'll want to remember and maybe link between similar ideas.

And then I'm currently trying to use it to make a solution to sketch out my Savage Worlds RPG campaigns. It gets a little tricky but you can make templates, script buttons, and that kind of thing. If you're already comfortable with web stuff you'll probably catch on WAY better than I have.

You can also host it as a website, or on your server or whatever, to use it like any other wiki. There's also plugins to use Markdown instead of "wikitext."

There's also an excellent guide to learning it at https://groktiddlywiki.com/read/ . It's basically an online workbook using Tiddlywiki itself!

The community is also super helpful. I do wish it had a little more out of the box, but something about a customizable, portable, digital "notebook" that doesn't require an account or hopefully-supported-in-5-years application is SUPER appealing to me. It's quite underrated.

Also just for fun I wanted to share my favorite example someone's been working on for quite some time now, a heavily customized D&D wiki

https://intrinsical.github.io/wiki/index.html

Tiddlywiki can be a bit dense and the documentation is slowly improving, but there's so much potential!