Yes-ish, adjacent. Syncthing usually you use it to sync to your server.

Here I skipped the server part. I just connect two devices.

If they both use the virtual mountpoint

MountAlice and MountBob

They get an underlying SaveAlice and SaveBob on disk.

so what gets dropped in MountAlice gets saved to SaveAlice, and appears in MountBob.

Once bob accesses it in MountBob it gets cached to SaveBob (like saved persistently to disk). But while the transfer happens a mmap is saved to disk to keep track of the segments that were transmited.

If changes happen on Alice for the file, GetAttr metadata is synced when the filehandler on Alice is released. and Bob knows to request the parts of the file that changed.

It did not go for the full-on folder sync. I went for a synced filesystem while the peers are connected.

And because ios and android do not have FUSE, i also added the option to add a file/ pull a file, that does the same thing.

So now, you can add folders/ files on android/ ios. and mount them as a filesystem on your desktop and do magic with them, and if they get changed you can export them back from the phone to the gallery or w/e files