I'm checking out Sphynx.chat which @jack just tweeted about.
It appears to be a way to chat over LN. I know they were working on that technology but I did not realise that it was implemented.
Does anyone know much about the tech behind it? Is it truly all living on the LN or is it reliant upon the Sphynx server?
It is truly LN native. But there are "custodial" plans that the Sphinx folks sell. You can run your own server. Most of the Lightning node in a box distros offer it.
I am doing HUGE transaction volume based on this tech through my node since i have set my fees to zero when going to the podcastindex node (Adam Curry).
Breez has also implemented some crossover stuff... not the chatting, but the podcast/streaming stuff.