Social Networks
A social network is a social structure made up of a set of social actors (such as individuals or organizations), sets of dyadic ties, and other social interaction between actors.
Bookmarking
Social bookmarking is a centralized online service which allows users to add, annotate, edit, and share bookmarks of web documents.
Social News
A social news website features user-posted stories that are ranked based on popularity, as voted on by other users of the site or by website administrators.
Media Sharing
Media sharing sites allow you to upload your photos, videos and audio to a website that can be accessed from anywhere in the world.
Micro Bloging
Microblogging is a broadcast medium that exists in the form of blogging.
Forums and Blog comments
With both blogs and forums, you can post a comment and reply to other comments, thus developing discussions.