There's also Dumb Pipe and SendMe which are demos (I believe) built on iroh to showcase some of its uses, and at the workshop we were shown a video of a startup using iroh for video game streaming (something similar to the old OnLive).
From what I understood (in spite of my lack of networking knowledge) and if I remember correctly clients have to be on the same relay (I think there's one for Europe and one for North America) and they use the Bittorent DHT Mainline (I had to google the iroh blog post about it because I forgot the exact name) for discovery. There was some stuff about BGP too, but it went over my head sadly.
I hope somebody more knowledgeable chimes in because iroh is really exciting, I feel like I could throw together a p2p application and it wouldn't be a daunting task due to it.