who can reply

 who can reply  is a 2020 feature of Twitter that allows the author of a tweet to explicitly choose from a set of options of which accounts Twitter will allow in their UI to reply and thus show replies from; the IndieWeb equivalent could be implemented with some combination of allow lists and Vouch.



Screeenshot of a Twitter iOS tweet writing UI with the "Who can reply?" menu expanded showing:
 * 🌍✅ Everyone
 * 👥 People you follow
 * ＠ Only people you mention

Limitations
This feature is a per-tweet setting that must be configured before posting.

Limitations:
 * Can’t change it for a tweet after you’ve posted
 * Can’t set a different default (e.g. "People you follow") in your settings, you have to set it per tweet every time before tweeting
 * Can’t set who can reply in Twitter posting APIs. Their APIs do not yet (as of 2021 June) support "who can reply" or otherwise limiting who can reply to your tweets. https://twittercommunity.com/t/choose-who-can-reply-to-your-tweet/156174