These are very cool p2p projects with nice NAT traversals.
https://syncthing.net/ https://github.com/hyperswarm/hyperswarm (whole family hypercore, hyperdrive, hyperswarm, ...)
https://syncthing.net/ https://github.com/hyperswarm/hyperswarm (whole family hypercore, hyperdrive, hyperswarm, ...)
All peers simply lookup their external port via STUN and publish this information.