RSS is pull only. It probably serves 80% of needs for most people ("I want to know when so-and-so has new content without manually going to the site") but Activ

RSS is pull only. It probably serves 80% of needs for most people ("I want to know when so-and-so has new content without manually going to the site") but ActivityPub does a bit more: - pushes content to subscribers in real-time (doable with RSS with WebSub https://en.wikipedia.org/wiki/WebSub https://en.wikipedia.org/wiki/WebSub) - allows content to "swim back" to the publisher: comments, replies, retweets/boost (doable with WebMentions https://www.w3.org/TR/2017/REC-webmention-20170112/ https://www.w3.org/TR/2017/REC-webmention-20170112/) - defines a protocol for posting to an AP-enabled endpoint (doable with micropub) AP defines a lot of things but doesn't do it well (see https://schub.wtf/blog/2019/01/13/activitypub-final-thoughts-one-year-later.html https://schub.wtf/blog/2019/01/13/activitypub-final-thoughts...), because it is not strict enough in what constitutes valid content. There are alternatives, listed above, that already do the work but they are centered towards everyone having their own server and going from site to site to post comments; the real appeal of AP solutions is that they're an all-in-one blob you connect to, and from which you do your browsing. The indieweb people (responsible for the alternatives above) have come up with "social readers" to enable this and have made a few propositions already: see https://indieweb.org/social_reader https://indieweb.org/social_reader (https://aaronparecki.com/2018/03/12/17/building-an-indieweb-reader https://aaronparecki.com/2018/03/12/17/building-an-indieweb-... in particular)