Iroh allows you to do NAT traversal (holepunching) using a relay to organize the rendezvous needed. But it is not opinionated about how to find the relay a node is using, so usually you give someone a "ticket" that contains your node id, authentication and the relay you are using.

Then they have a pluggable discovery layer to find nodes relays in a more asynchronous way. The first discovery mechanism they offered was just centralised DNS server they run. The second was Pkarr itself, and that is what is used in the mentioned p2p social media app over Iroh.