I too am still using BTsync. Something else you can do to help it stay local is uncheck "Use relay server when required", "Use tracker server", and "Search DHT network". Make sure you have "Search LAN" checked.

Those settings are in the preferences for each shared folder.

Try the open source equivalent of BTSync, Syncthing
https://syncthing.net/
https://github.com/syncthing/s...

I haven't used the POS portion, but OFBiz is a very flexible open-source project that does include POS.
I've used other portions of the project and once past the learning curve, it's great!