Yes.
And in no particular order…
Syncthing documentation:
- SSH Tunneling (conceptually similar to a Tailnet)
- Security Principles
- Relaying
- Syncthing Relay Server
- Syncthing Discovery Server
- Firewall Setup
- Advanced Configuration
Syncthing forum:
- why does syncthing transmit my files over the internet?
- completely disable internet access
- Run on wifi without internet
- Sync over LAN without Internet
- How to connect between Windows and Mac privately without internet?
- Can Syncthing Sync over LAN if no internet access is available?
- Setting up in a LAN with Internet granted to one machine only
- Is it possible to use Syncthing with no internet access? And is it possible to have all changes go through a single server?