“
SyncThing” — a cloud-free, cross platform, open source, peer-to-peer folder synchronization solution.
This thing takes a bit of getting used to. It's way less user-friendly than sync.com (which I would and do recommend to anyone and everyone). But if what you want is something of a “Swiss Army Knife” folder synchronizer, than SyncThing will probably do anything you could want.
I'm currently using SyncThing to synchronize selected folders of two Drobo NAS devices at different locations. And separately, I've set one of those Drobos to maintain synchronization among a network of 20 remote laptops being used to provide clinical home neurofeedback. Each of those laptops has a one-way (Drobo to laptop) folder sync from a common directory on the Drobo, and individual two-way sync's between selected folders on each laptop and it's own Drobo-sync'ed mirror folders. Like I said, SyncThing is a Swiss Army Knife solution that can perform pretty much any sync task that you could imagine.
SyncThing lives here:
https://syncthing.net/ and as with the “Sync.com” service (see previous post) I recommend it without reservation so long as you're willing to invest some time in figuring out how it works.
If you want to know more,
the Security Now! podcast #734 has all the details!
