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LocalSend - Share files to nearby devices
(localsend.org)
This is a most excellent place for technology news and articles.
I'd use pairdrop over this so I don't need to install it on all my devices.
https://docs.linuxserver.io/images/docker-pairdrop/
i prefer pairdrop specifically because there's no install.
however, looks like local send (after install) might work offline as long as they local network is up.