it's not centralized, you can choose your smp, xftp and webrtc ice servers, or you can install them in your own server

so is a decentralized chat application

so far i was able to do calls and videocalls to everyone (i have 8 friends there), but i won't say that the calls are stable, the application needs time to stabilize, and that's what they are doing, you can check the the GitHub page or chat with the developer if you want to know more