I've been following Holepunch developments for a while. There does not seem too much publicly available about who's building with it, but I personally regularly use Holepunch's Keet[1] for video calls with friends in parts of the world with censored Internet. I'm able to chat with voice and image quality surpassing anything else I've used.
It's frigging cool. It's super hard to make a meaningful model for p2p applications because they need all kinds of data structures that are research tier or have scarce real-world data. It's not just connectivity that's hard. If they manage to do everything decentralized and create meaningful constructs. This could be the start of actually realizing all the rhetoric these kind of projects have been promising. This seems to have technical merit, imo.
[1] https://keet.io/