Didn't know about Syncthing but it reminds me about Infinit, it had the exact same features 7 years ago (P2P sync with simple ID for registration). It was bought by Docker [1] and pretty much disappear I think.

I just checked Syncthing, seems pretty old also (8 year for 0.1) !

[1] https://www.docker.com/blog/docker-acquires-infinit/