the main bit holepunch is https://github.com/holepunchto which you could use to intergrate with a nostr app, keet is not yet but has been promised to be opensourced, they have a big update with notably a new data structure to support 1000's of users in a chat room and phone calls on mobile, i think opensource will come soon after

given tether has billions in profit from usd holdings which they are using for this i think its something to be hopeful for because p2p has the potential to displace all big tech