Interfacing markdown:

• Joplin (pretty popular, haven't used)
• Standard Notes (same as above)
• Markor (feature-packed, a bit outdated)
• BeautyXT (maybe a bit too minimal almost, but gets the job done if you just want text based editing)

Interfacing orgmode:

• Orgzly (beautiful simple app that uses a superior syntax when compared to Markdown due to its built-in agenda and to-do structure)

Syncing flat files (might not be compatible with all of the above)

• Their own hosted server if available (easy but not private, some provide E2EE)
• Syncthing (easy and private)
• WebDav or an SFTP server (hard if self-hosted or otherwise easy through some providers)
• Termux + a Git server (pain)

Not FOSS, but I use Obsidian, and is FOSS, SyncThing for syncing.

There are FOSS Markdown editors of course, I just prefer Obsidian.

I use Markor on android, plus a self-hosted instance of codeserver for editing online. Synced via syncthing. Sometimes i use Obsidian with the same synced folder.

I finally got fed up with Evernote's increasingly aggressive paid upgrade requests. It would flash an "upgrade special" every time it opened and a followup, "Are you sure? You won't be able to get back to this offer". Like, please, let me not get back to the offer ever again.

I have been using Joplin with Dropbox sync. The UI is pretty good on Android and windows. Markdown input is easy to manage, it does checklists well (you can check and uncheck the boxes without going in to edit the note). The folder structure for organizing notes is good.

Not being able to share notes with other users is the main limitation. My wife and I have solved this by syncing with one dropbox account on with phones and computers and just having a folder for each or our personal notes plus the shared notes. But really it is all shared. I don't consider this ideal, but it's workable for now.

The dropbox sync is kind of slow / not very good if multiple people are making edits in real time, but I had this problem with Evernote too.

I think you can get more functionality out of the Joplin cloud sync, but I am already paying for Dropbox.

I use notesnook

If you have a nextcloud instance, and you don't need Keep's collaboration features, Carnet is FOSS and is a decent solution

Together with the other suggestions jtx board is also a new addition Developed from the davx5 team , tasks,calendars,journals and NOTES.

The good: Easy sync of notes with any caldav provider . No extra servers and apps for tasks,cakendars,journals. Mtls support ( davx5 supports it ) for extra security if you selfhost

The bad: No desktop client

Standard notes or Joplin have apps with versions for both phone and the desktop.

Other options:

1. Markor (Android) - Syncthing - Zim (desktop)
2. Orgzly (Android) - Syncthing - Emacs orgmode

If you have a Nextcloud instance, you can use QOwnNotes (desktop) and Nextcloud Notes (Android). You can also access notes on the web.

Even though it has more a journaling/daybook feel, I use LogSeq for this. Their paid version offers cloud sync which is perfect (and easy enough) for me

I use zettel notes and sync with syncthing. On pc I use neovim with marksman and zk.nvim

Moe Memos is a pretty nice self-hosted solution as well. https://memos.moe/

im using QuillPad currently. it seems to have Nextcloud support, though i havent set it up personally. nice ui and markdown syntax

Anytype :)

https://doc.anytype.io/anytype-docs/intro/readme

https://github.com/anyproto/anytype-ts

Has a desktop and mobile app. You create an ID which is loads of words stringed together. You can use that ID to decrypt and access your data. If you lose that secret your data is gone.

Joplin + Syncthing