Here are the some main categories that come to mind for business and social networking for (1) business;  (2) friends, family (3) information.  You will see they can also be broken down in venue of delivery:  text, tweets, photos, videos, professional graphic-art ads; and what you can invent in the future.  The target audience also determines if they live or die.  Attract too much of the ‘wrong crowd’ and the site will not blossom with professionals.