Anyone with the link can jump in and write, live, same as a Google Doc share link — but the live sync happens over an ordinary WebSocket relay (this Worker), because that's the part atproto genuinely doesn't solve on its own: fast multi-writer text merging needs a coordinator, and a signed per-writer repo commit isn't built for that. What can live outside a corporate silo is the durable copy — sign in and snapshot the doc straight into your own PDS whenever you want.
Honestly: not the real-time part, not yet, not without a relay somewhere — nobody's solved keystroke-level CRDT sync over the firehose. This is the closest good version: a live pad for the collaboration, with atproto doing what it's actually good at — being your copy of the thing, in your repo, that no product can revoke, paywall, or quietly change the terms on.