close friends

 close friends  is an explicit set of followings that some social media silos allow you to choose as a limited audience for some post types, like Instagram story posts.

IndieWeb Examples
none to cite, however there has been enough discussion and prototyping of this over the years, using IndieAuth / Web Sign-in as authentication, that there are some out there.

Instagram
Instagram supports a close friends feature for story posts.

needs screenshots of UIs:
 * viewing someone’s profile and adding/removing them from your close friends
 * viewing your list of close friends
 * removing or adding to it via suggestions
 * creating a story and the two buttons at the bottom to post to "Your story" or "Close Friends".