I'm curious to try Sphinx Chat which is directly based on the lightning network.

I'm sure it's possible to fork it to add Nostr integration. Some useful shit could be done with that outside the obvious connecting npubs and NIP-05's, for example using Civ Kit or similar to create a P2P market for using someone else's node to onboard yourself.

Gonna give it a go myself when my new Start9 node is synced up.