The Social Web Working Group has published Linked Data Notifications (LDN).
LDN provides a mechanism for passing notifications around between clients and servers. Notifications can contain any data, and are expressed in RDF. The contents may be used internally by the receiving system, or exposed to a user through a consuming client application. Any resource can advertise a receiving endpoint (Inbox). This is a core building block for interoperable decentralized systems, as it enables servers (which may be personal datastores) to expose endpoints for receiving notifications from both client applications (like social network sites) and other servers (like nodes in a federated social network). Furthermore, the notifications
are uniquely identifiable and reusable by other applications, so the data can serve multiple purposes, and people are not locked into using the application which originally generated a notification.
LDN is already demonstrated to work well with several other existing W3C standards, including the Web Annotations Protocol and Vocabulary, and Linked Data Platform servers can serve as LDN receivers out of the box.