RSS / Atom / WebSub, IndieWeb, and ActivityPub aside, am I missing actively-used open protocols and standards for subscribing to published content?
@benwerd I think the email protocols (SMTP/IMAP) fit the actively-used, open, and subscribe to published content criteria. I'm not even joking. 😊 Email newsletters are still a thing, and you can subscribe to content updates via email in feed readers like Feedbin. JSON Feed is worth mentioning as well. I don't know how actively used it is, though.