[andai]

If it's for internal use, I have had good results with Resilio Sync (formerly BitTorrent Sync).

It's like Dropbox except peer to peer. So it's free, limited only by your client side storage.

The catch is it's only peer to peer (unless they added a managed option), so at least one other peer must be online for sync to take place.

[microtonal]

They don't really maintain the regular Sync client anymore, only the expensive enterprise Connect option. My wife and I used Resilio Sync for years, but had to migrate away, since it had bugs and issues with newer OS versions, but they didn't care to fix them. Let alone develop new features.