Arguably Google+'s Circles were pioneered by XMPP thanks to roster groups (https://tools.ietf.org/html/rfc6121#section-2.1.2.6 https://tools.ietf.org/html/rfc61

Arguably Google+'s Circles were pioneered by XMPP thanks to roster groups (https://tools.ietf.org/html/rfc6121#section-2.1.2.6 https://tools.ietf.org/html/rfc6121#section-2.1.2.6), which can be used for PubSub to only allow members of a given group to retrieve elements from a given node. So you'd publish stuff for your friends group, for your family group, ...