Vertical social networks.

The users form communities who have reasons for using the application, and these can be personal or professional. Include:

• Sharing professional information: The most popular is LinkedIn, for all types of professionals.
• Sharing general information: People can creeate private groups to sahre information about projects, organise events and exchange photos or experiences with their friends. An example is FriendFeed.
• Sharing photos: Some popular applications are Instagram, Flickr and Pinterest.
• Sharing videos: Few common examples are Youtube , Dailymotion and Vimeo.
• Live streaming: Skype, Twitch.tv, Livestream and Upstream.tv. 

There are othr services associated to sports,cinema, books and other topics.