Not really, but there are tricks and hacks here and there that implement this functionality at least partially. The thing to start with for better understanding of this concept is outliner. Another representation of similar entities may be, say, mindmap, but mindmaps really suck at small screens.

Once you start with the outliner, imagine you can link just any entity to any and every PIM object is linkable entity. Once it is done, all "frontend" human interfaces whould work seamlessly following the links.

Say, if you open a contact card, you magically see:

conversation history (email, IM, call and dictaphone records)
meetings, todos, projects
places
photos
documents shared, exchanged or discussed with this person
social network updates

Same thing happens if you open an appointment. Or a location. Or todo entry.