Not really a social medium but a brilliant example for digital storytelling. With the StreetMuseum iPhone app from the Museum of London you can look at historical views of the city while you walk through London.
Personal Narrative Example- created with WeVideoOur team got a chance to experience this hands-on when we participated in a workshop facilitated by The Center For Digital Storytelling. Learning from their 20 years of experience in storytelling allowed us to find better ways to write, create and share our personal stories. Here is my story from the workshop: