Syncthing runs locally, you don't run a separate server with it (although you can, as another participant in the list of clients). When two clients see each other on a local network, or over the internet when you allow the use of the open discovery servers, they sync data. There is no cloud or central service (beyond the optional use of the global discovery servers).

You don't have to maintain anything beyond setting it up and reconfiguring the clients allowed after reinstalling the OS on a client, and occasionally checking on it and updating the software. It's pretty low maintenance.