@okpierre@evan@Mushi the license you pointed at concerns the distribution if the at protocol reference implementation. The propietary character of the protocol itself is a different matter.
@evan@Mushi it seems to me ATProto’s descentralization is mostly theoretical (it is not realistic for a person or a small organization to run the main aggregator service and indeed no one but bluesky does) whereas for ActivityPub is not only possible but a reality.
If Bluesky were to dissapear today, all the self-hosted PDS instances would be rendered useless immediately. If Threads or the biggest mastodon instances closed today, the fediverse would still be alive and kicking.
I just finished a first read of @evan ‘s ActivityPub book from O’Reilly. The definitive guide for anyone who wants to write applications for the fediverse, imho. The detail level is spot on.
@atomicpoet regarding 2, I think its itended to be extensible with new lexicons:
"[...] Bluesky currently supports a micro-blogging mode: the app.bsky lexicon. Developers who create new lexicons would likely deploy a corresponding App View that understands their lexicon to service their users. Other lexicons could include video or long-form blogging, or different ways of organizing like groups and forums."