I don't know of anything specific, and StackOverflow is not the place for generalized library recommendations. However, it should be trivial enough to implement yourself. Activity streams are composed of four main components:
For example: "John (actor) shared (verb) a photo (object) with Mary (target)."
Just create an entity that can track these four aspects, and then add a record describing the action each time something happens. By making certain parts foreign keys (actor/target could be foreign keys to your user table), you can then pull actions specifically related to a particular user or other object in your system.