Yes. You have a "share". That's the imaginary dropbox-like thing. Then you have a folder on some device that you link to that share. All folders you link with that share become the same on any device, intelligently.

For sanity's sake, unless I'm doing something like syncing game map folders across devices but inside a game's special map folder, i keep them all in a folder called 'sync', and name the folders in 'sync' after the share name. Otherwise, things can get wonky. Consistent naming is important imo. With a share called "share with bob" started from a folder called 'bob sync' on sam's end, 'Sam' on bob's end, and they stay that way after anita joins, and she calls it 'bob and Sam' or something. Someone else joins and calls it "buddies". Then, people say things like 'i put it in the sam folder', and it brings up questions.

But with a little bit of organization, it's awesome. Drop a file in a folder, and it's now on the other person's computer too. They move it out, and the file's gone for you.

If the computers can talk to each other (same lan, or proper internet connection) they will. If you have dysfunctional NAT or phones with no public-facing IP that are connecting to each other, just make sure some system can be accessed, and it's all good. You want a cloud backup? Just set up the daemon on a server somewhere, and join the share.