Syncthing? I'm taking 'offline' to mean 'not requiring the internet', which means you can have plenty of computers!

I use seafile for this. Some people dislike that it has proprietary storage but you can backup from a fuse mount

Samba share?

Old technology still works, even if it is old!

Works so great on new devices like smartphones. Except not.

And so easy to set up on a home computer. Except it's not always on and doesn't come with backups.

I'm not saying S3 is where it's at but might need a bit more than just Samba. Or maybe you don't but people who need Dropbox do.

iOS has native support for SMB in the Files app

Turning on SMB is usually just a click of a button, even macOS supports it

Any user technical enough to be able to set up an S3 bucket, Syncthing, Nextcloud or this "Locker" tool from OP can also set up an SMB share

I was responding to the above thread, where sharing files on an offline network is being discussed. Backups were not mentioned as a requirement.

Yea, boy, you’d like to think.

But sharing a folder on my Mac with my wife’s MacBook has been a Google diving, arcane command line headache.

I would have thought sharing the folder, and marking ‘everyone’ for all the read/write modes would be enough. But, no.

I guess with APFS it’s a lot more fiddly. It’s not intuitive, and not in the info panel.

Samba, rsync, sshfs, even fusefs... but there's seemingly nothing that can keep your files yours across your own devices without extensive hacking/setup, suspicious EULAs, MitMs, etc. We can build it, but normies can't