Oh I see. syncthing is more for keeping 2 directories synched between machines. I guess in a sense, it's more of a Dropbox competitor while croc and sharr are for one-off file transfers. For awhile, I ran an owncloud server at work for internal use. It was pretty good for file synching, but required some port forwarding through the router. These solutions mentioned here seem to all have a public host somewhere to eliminate that need.