Here’s an idea.
- A web server where people log in with their social media details (like Twitter, or Facebook, or ..).
- The server doesn’t store the password, but it stores the Service (eg. Twitter) and the Username.
- The server pulls in the contacts from the Service, through the available API, if there is one.
- The Contacts then can be modified, exported, used etc. Other details can be added.
- To make it actually worthwhile, the server needs to go a few more steps. Using the Users details, try and find their other "presences". Their existence in other Social Media services.
It’s nothing more than a db of Contacts with relevant contextual information. That, and the logic to _find_ the relevant contextual information : ).