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OrgNote - mobile app inspired by org-roam and org-roam-ui (early beta)
(about.org-note.com)
A community for the timeless and infinitely powerful editor. Want to see what Emacs is capable of?!
For what it's worth, I collaborate with 1 other person, and for me it'd be sufficient if you simply alerted the user that someone else is currently editing the notes, locking them until the other user is done. What's a much bigger problem is if someone edits the notes offline tries to sync them later!