The second paragraph of their blog posts suggests Radicle doesn't support central identity. It's really hard to imagine one of the core concepts of Radicle bending (breaking) to allow that.
Building on this, I think Radicle would be described as "peer-to-peer", whereas something like Tangled is "federated". The article differentiates Tangled from other federated systems by saying that you can use a "centralized" ID using AT Protocol, but I don't know if the ID provider itself is centralized, centralized-but-self-hostable, or federated.
atproto uses the DID system, which precedes it by a few years. at the moment, 99% of atproto users have a centralized id from the did:plc database, and a few dozen use did:web. no other DID methods are supported in the tooling yet afaik.
