There are public ICE/STUN servers that can facilitate NAT-punching, google even hosts one. But that's not the aspect that I thought the root comment was talking

There are public ICE/STUN servers that can facilitate NAT-punching, google even hosts one. But that's not the aspect that I thought the root comment was talking about, but more the aspect of "A is hosting a room called 'stuff', and B and C want to browse the list of rooms and connect to it".