Looking for OneNote Alternative

I use Joplin and sync the notes between devices (including Android) with Syncthing. There's lots of other options for syncing, but I already had Syncthing set up and liked it
- Joplin is amazing. I think I have it syncing through OneDrive (I don't use OneDrive or any Microsoft products so I'm not sure why I did that), but it has so many options to sync using things you may already use
- I use the same setup: Joplin and SyncThing. Works well on my macbook and windows boxen.
- I moved from Onenote to Joplin, and it's been faultless. I'm using a free dropbox account for syncing and that works fine too.

I selfhost my Joplin server and use the clients on my Linux desktop, my windows laptop, iphone and Android. It is definitely one of my favorite selfhosted apps. To prevent any issues with sync, the first thing I do when I open the app is to click the Sync button and do the same when I close the app at the end of the day. This way I ensure that I am always working with the latest version. It has not failed me so far, considering I am a very heavy user and have quite a few notes running at any given day.
- And I'm another who self hosts Joplin. My wife and I use it on our desktops and mobile devices. We specifically switched to it from One Note and it's been perfect for our use!
  I used it extensively as I was writing (I'm an author) to make notes about things I needed to go back and correct, or an idea to incorporate, etc.
- Interesting I didn't know you could even host a server for it. I use Joplin with local files and nextcloud to sync them I'll have to check that out
  
  you can sync them with dav on nextcloud, then joplin takes care of pushing and pulling but the files are on nextcloud

Create a folder, put markdown files in it, sync* and backup* the folder however you like and edit the files with whatever you like*.
Within my folder I have a daily journal - start each day with a list of what I hope to achieve today and make notes throughout the day as I progress on those tasks. The next day that journal becomes something I'lll refer back to in the morning to decide what to do next. Depending on the project - weekly or monthly might be more suitable than daily. Or maybe something else entirely.
I also have folders an files for longer term tasks.
If you want to collaborate, make a second folder and choose a sync platform you can all agree on.
(* I use GitHub for Sync, Backblaze B2 for backup, and Visual Studio Code for editing, with extensions for markdown and making GitHub a little easier... specifically GitDoc for auto-commit/push/pull and Markdown All in One for formatting/etc. Also Copilot is handy for some note taking tasks. The "foam" extension mentioned here looks like it might be great too)

Check out Obsidian! The canvas feature is very similar to onenote snd obsidian in general is the best notwtaking app/ personal knowledge management system in existence
- Very much this. Obsidian has a learning curve. It needs more than a day to get a feel for.
- Obsidians great! I do wish it was open-source though :(
  
  I switched to Obsidian not too long ago.
  For my needs, Joplin was a good open source alternative.
  Between the two I went with Obsidian because, while the apps are closed-source, the data is accessible. All your notes are just stored in plaintext (with markdown) as simple files in a directory structure.
  Joplin, in contrast, uses a SQLite database which adds a layer of complexity.
- Obsidian is what I use mostly, it syncs great with syncthing across all my devices. It doesn't have drawing support, so whenever I need to doodle something I end up in samsung notes again.
  
  The Excalidraw plugin may do the trick.

As your description is rather short and does not really restrict the "recommendation space", I'll start the round of recommendations with Joplin
- I used Joplin on Windows and iPhone - syncing (encrypted) using a OneDrive account. So far working well.
- Joplin also has a great web-clipper through a companion addon in Firefox (and I assume also Chromium)
  Joplin is great in many ways, and I do use it to some degree, but there's a few things that irks me.
  Notes and attachments being stored in a database and referenced by a cryptic UID instead of plain files with human readable names makes integration with other apps impossible. And it's bad for data portability
  On Android I've never been able to get it to background sync. I need to keep Joplin in the foreground. The second I switch to another app it stops syncing
  On sync conflicts it'll just use the newest note as master and overwrite older changes. Luckily if you realise it happened you can use the history feature to get back lost changes. Typical scenario for me is to add much more stuff to a shopping list while on desktop. 30minutes later open the app on Android while shopping to tick off an item. Realize all the recently added items from desktop are gone to the ether (stored in history on the desktop and other synced devices)
  Hopefully these sync issues are some rare bug for me. I've tried all the usual "battery saving" tricks in android, but still Joplin will not background sync. Other apps like DavX5 sync fine. Are anybody else here having luck with Joplin on mobile?
  
  As far as I know it's a known limitation. Joplin just does not have background sync. It's ok for my use case but the initial sync can take a long time depending on your database size. Other than that, I'm happy with Joplin.

@IuseArchbtw I switched to Zettlr a few years ago and never looked back https://zettlr.com/ there are tons of markdown apps in other platforms that can give you the cross-platform feel but for desktop this is it for me

Logseq is my go to. It can be as simple or complex as you want, and it's open source under AGPL 3.0 which is really important to me.

I would suggest Logseq. It's excellent and a step up from One Note IMHO.
- I'm using it both for notes at work (software development) as well as a separate graph for my own thoughts, ideas, todos, pretty much everything. Using Syncthing to sync my graphs between devices works pretty well, though it's had a bit of a learning curve in getting it set up.

Markor on Android, nvim on Linux and sync with syncthing. Using markdown.

If you use vscode, the foam extension is great!
- Thank you! Trying it out now and it's amazing.

Joplin is great but Obsidian is definitely worth checking out. You can find both as flatpaks.
- Big fan of Obsidian. Especially for written notes. If you are working with a lot of images I'd give its canvas feature a try. I'm not using it personally, but I think it might fit the bill.
  
  I dont use canvas, but I deal with plenty of images and screenshots. I usually just have a topic top level folder that contains notes and a nested media folder that I store the images in and link to them