I haven't tried yet (because I'm not a very organized person) but pushbullet.md

Eidos – Offline alternative to Notion

Plain text files.

Don't count standard notes out just yet!

They offer discounted plans upon request!

https://standardnotes.com/help/56/what-if-i-can-t-afford-the-price-of-extended

I use Docbase, which apparently has been archived on GitHub.

https://opensource.appbase.io/Docbase/

https://github.com/appbaseio/Docbase

It's not strictly privacy-focused but The Goblin's Notebook is designed exactly for your use-case. It has markdown, object connections, every object has a player visible setting, so your players can access known content while you keep secrets hidden. There's a free tier, a mid tier at $1.50 and an unlimited tier at $3 dollars a month (managed via their patreon).

I use Obsidian, which is quite powerful with their vast plugin library. You can do a lot of automation, and you can check out some of Nicole van der Hoeven's videos, who among other things use it to keep track of TTRPG campaigns, both as a player and as a game master. For example this one.

I don't use their sync service, but have all files locally on my Nextcloud server. I sync them to my phone with Syncthing, which unfortunately means I cannot encrypt them with Cryptomator like I planned, but if you only use it on your computer, that is also something you could do. If you are paranoid about them still phoning home with your data, then you can block its network access with a firewall. I think you can install plugins manually.

I would have preferred it if it was FOSS. I have considered checking out Logseq as an alternative. But the bullet-based workflow doesn't appeal to me, so I haven't tried yet. I switched over from Standard Notes, and honestly it was pain to transfer because the text export from Standard Notes was all over the place, as I had used a lot of different note types. I tried to parse some of these smart notes they have, but I couldn't quickly figure out how they were structured to automate it, so I ended up manually going through and copying over what I wanted to keep. I like the approach of keeping plain text markdown files. It is easier to export to another application in the future, although some of the content will be useless as it is explicitly written for the plugins (e.g. Dataview).

Obsidian and logseq

For taking campaign notes, bookstack might be an option. It is specifically organized in a book, chapter, page hierarchy.

I also use it for my journal and to do list just because I already used it. Probably not as full featured as obsidian though

How about Notesnook? https://notesnook.com

Open source and end to end encrypted

I'm using Trilium notes. it's simple enough and does what i need. Used to use Obsidian but wanted something open source, and with Trilium you can self-host the sync server for free (even comes with a handy web-ui).

Note that it is much simpler than obsidian, but for me it's plenty. It was easy to import my obsidian vault into it, and it allows exporting as .md files which work fine back in obsidian too.

Recently the dev said he's putting it into maintenance mode, so no new features will come to Trilium. There's a community around Trilium Next that wants to keep expanding it, but personally i hope Trilium stays as it is and is maintained for a long time.

I had this exact problem a whole ago, trying to find an alternative to OneNote. I went through many of the other suggestions in this thread but settled on Trilium.

Super easy to setup in a docker container. Self hosted so I control my data and access. Can by accessed via reverse proxy when I'm out and about.

Notes can be a mixture of text, pictures, code (with formatting based on language)

They are arranged in a directory structure with notes inside other notes under chosen topics down the left, and open notes are in tabs along the top, much like One Note.

The chrome extension allows me to quickly snip and send back screenshots or Urls of sites I'm on, and the android app let's me make quick notes which are filed away by date for later organisation (when I get round to it...)

The only thing it doesnt support, that I wish it did, is multiple users. I don't see why you couldn't just make another container for each user, just not very practical if you have a lot of users.

org-mode/org-roam-ui in Emacs with PGP support synchronization via git in forgejo

I had almost the same question. So let me quickly share what I came up with.

I have a ton of notes in different areas. By I was not happy with the way Obsidian worked – synchronization specifically. I didn't want to pay for it. So I got on a quest for the perfect note-taking system. It had to be:

• Markdown-first. Because we all know why;
• Interoperable. That is as few additional flavors and things added as possible;
• Portable. Such that I could open my Notes folder in any app;
• Synchronization. With as few additional crutches as possible.

Main text editor

Desktop. I use [email protected]. It has marksman LSP (meaning markdown support out of the box). This is how I know no other app is involved into writing process (no telemetry, etc). Also zero task switching this way. I still use [email protected] from time to time. I don't use Logseq because it has opinionated file structure, which doesn't meet my interoperability need. Also, I don't always need an outliner. You can turn this feature on in Obsidian, but you can't turn it off in Logseq.

Mobile. I use the simplest markdown-capable apps for iOS and Android. Also, don't forget Cryptomator.

Sync. For the most part I use [email protected] to sync all the notes. Such that they are not uploaded into any cloud storage. I don't use iCloud, or rather almost never use it.

As for your question. Obsidian is a pretty good choice because of its extensibility, portability, and interface. Although it easy to get lost in the plugin rabbit hole. Its desktop and mobile (if you go for it) privacy policy is pretty solid. Client-first markdown app – nothing more and nothing else.

Lastly, there is this idea that one needs to sync notes via some cloud. Not true. You should consider your threat model first. Cloud sync is not must. In some cases, Syncthing is more than enough, is more private, and might be a more secure option (as it reduces your surface of attack to some extent).

I guess that's all

You can read Obsidian's privacy policy. Basically, everything remains on your device unless you pay to use the Obsidian Sync. I switched from Standard Notes to Obsidian last year and I haven't looked back ever since. You can use Syncthing to synchronize your Obsidian Vault across multiple devices. All you need to do is add the Vault directory to Syncthing, that means you need to first make a dedicated folder in your filesystem for the Obsidian Vault which you will be required to do anyway while setting up Obsidian.

crypt.ee

I use logseq for work notes and Obsidian for personal. Obsidian is more markdown which I like for my loose notes. logseq, on the other hand, is more focused on productivity and it's fully opensource. Obsidian is only free for personal use, however their notes being closer to standart markdown means that they could be openned with any text editor and be just as functional.

Syncing between computers is easy – it's just a git repo. Dealing with mobile is tricier but I never needed it so can't comment much.

Outline is self-hostable.

Anytype

Since you're specifically looking to replace OneNote, you might want to take a look at BookStack. It has similar organizational concepts, and I think it's FOSS.

There are many open source wiki softwares: zim, dokuwiki, etc.