Linux

Joplin has multiple sync options. Other than Nextcloud, you can use OneDrive, Dropbox, and they have a subscription service as well.

Obsidian is another to look at, but you need to either pay for sync or bring your own sync (~~though I don't know that you can sync to mobile without using their sync~~ edit: see below comment by @fossisfun@lemmy.ml that explains how to do it).

I think it's probably helpful to know if sync across platforms is important to you, and if so, whether you're willing to pay for it. I'm not sure that there are really many alternatives to an app provided for free with free syncing - that costs money to provide and honestly I'd be a bit dubious about using a service like that.

Emacs + orgmode + org-capture + deft + orgzly + syncthing

Sexy Stallman pose

I just sync a directory called "Notes" everywhere and use whatever text editor is most comfortable on any given platform to edit Markdown documents. Helix on desktop, Markor (or, increasingly, Simple Text Editor) on Android. For checklists, same thing except I use todo.txt for the file format, and the todo script on the desktop and Simpletask on Android.

I have been looking for a self-hosted, concurrent collaborative web editor, as asking my wife to write Markdown is a bit much, and the syncing becomes more complex, but I haven't settled on something.

Logseq good alternative to obsidian Use syncthink or save the files to drive for syncing

Obsidian is a brilliant note app, it's free provided you setup your cloud sync solution (I use syncthing) as it just creates .md files that you can do whatever you want with

For note taking, Joplin is pretty good, in fact I went from Simplenote to Evernote (over kill and not free) to Joplin using Dropbox for the syncing (syncing is done by Joplin, so you don't need a 'syncing' app) between my PCs, all Linux and my Android phone. Simple to set up and free. I do not use it as a Journal as that is extremely poor, but for notes, it's perfect

Joplin + Syncthing is great, as other people suggested.
I keep it even more simple: I write stuff in markdown, share my .md files with Syncthing and edit them with markdown editors.
The best I've tried so far for Android is Markor, while on Linux I either use Ghostwriter (on KDE) or Marker (on Gnome)

Maybe Notesnook? There's a free version and they also offer a payed plan if you need more options.

You don't need your own server to use Joplin. You can select a local directory to store your notes and sync this directory with Syncthing between devices.

I am not sure if this works with iOS though.

Just sync .text or .md files using syncthing. Total control!

Agree about Joplin. No need for a full NextCloud instance, I use the WebDAV option which Apache has pretty much out of the box.

Notesnook and Standard Notes are really good. Both are end-to-end encrypted and FOSS.

Every other app and solution I've tried is kinda janky, e.g. using Dropbox, git, Syntching or some other app to sync across devices. I want an all-in-one, encrypted, cloud-based, FOSS solution.

I've been using Standard Notes for some years now and I'm pretty happy with it.

Biggest issue with Joplin is that it doesn't store the actual markdown in files that I can see. You're basically screwed if you ever want to move to a different product.

Trilium with trilium web clipper plugin, moememos with its web plugin and linkding with its plug in. Been able to keep up with all notes with this trio

If you want it to be truly multiplat and want to control it, you either need a self-hosted web service (simple as a basic wiki or as complex as nextcloud) or just sync plaintext markdown files and use an editor on each platform. Anything else and you'll just eventually end up in the same situation.

TiddlyWiki — a non-linear personal web notebook

TiddlyWiki, a unique non-linear notebook for capturing, organising and sharing complex information Use it to keep your to-do list, to plan an essay or novel, or to organise your wedding. Record every thought that crosses your brain, or build a flexible and responsive website.

TiddlyWiki lets you choose where to keep your data, guaranteeing that in the decades to come you will still be able to use the notes you take today.

https://tiddlywiki.com/

I use Trilium

@OrkneyKomodo
I use #syncthing as an alternative to cloud services. Share two folders, no matter where they are, on what device etc, provided the device can run a version of syncthing.
And its not only notes: pictures, movies and whatnot.
I transfered 60gb of pictures from the family oc to my phone with that

Years ago, I was looking for something similar. Used turtl for almost a year before switching to Joplin. Joplin was great, but not quite what I needed, and when Logseq came around, I switched again to it. Again, Logseq was just not exactly what I needed (though it is pretty powerful!) and I was worried what would happen when the devs either made it paid or abandoned the project, like so many before it.

The solution to my woes was Emacs. Now, I won't pretend the learning curve isn't steep, but there just isn't anything that compares to it. Org-mode + Org-roam + notdeft is amazing, and I've never even looked for anything else since becoming accustomed to it. Plus, you can easily modify the existing tools or write your own to adapt it to your personal style.

You will never regret the time you invest in Emacs.

I use Zim, a local wiki which uses text files with a markdown-like syntax, Syncthing to synchronize the notes, and Markor on Android supports this syntax.

I've been using silverbullet.md but it's self hosted

I've used vim with a smattering of essential plugins for years to do this, and only this year moved to Neovim for the same.

It's not Open Source, but I've also taken a hefty liking to Obsidian's canvas mode.

I have been using QOwnNotes for about 6 months. It is cross platform, lightweight, extensible and a plain-text markdown note-taking program written in C++/Qt. It can integrate with Nextcloud. Installable via scoop on Window and apt on Debian† (after installing their apt key).

Author is quite responsive on GH issues.

† Also most major Unixes

Obsidian and a shared Dropbox/Google Drive/OneDrive folder?

Turtl

Been using Joplin for ages, absolutely no dramas with it at all.