It is completely decentralized and works like Tor (Onion Routing) while others are centralized or federated.
It is based on the signal messenger, the apps look nearly identical.
And you don't have a phone number or an account login, you just have a long UID that you use like your phone number and a random recovery phrase. It is all about not sending much metadata about you, your phone, etc.
More decentralized and censorship resistant than Signal, which that is sitting on Google's servers. Google has the ability to shut Signal down if they wanted to or if asked to by the authorities, since Signal is helping others evade sanctions illegally without a license.
Signal also has a private cryptocurrency attached to it, most definitely used by criminals, scammers and even pump and dumped by the founders which one of them are the founders of Signal. (Yes. Moxie is part of it.)