Facebook is the world’s largest social network, with over 400 million users. Facebook was founded by Mark Zuckerberg in February 2004, initially as an exclusive network for Harvard students.

MySpace is one of the world’s largest social networks, with about 125 million users. Originally inspired by Friendster, MySpace quickly grew to become the world’s largest social network, before being overtaken by Facebook.

Friendster is a social networking website. Its headquarters are in Mountain View, California. The service allows users to contact other members, maintain those contacts, and share online content and media with those contacts.

Founded in 2003, hi5 today is one of the largest social entertainment sites in the world, with approximately 50 million monthly unique visitors who use the site to stay connected to friends, meet new people, share photos, and play games.

Launched in July 2005, Bebo has steadily risen to become one of the world’s most popular social networking sites. Users can create profiles on the site for free, stay connected with friends, watch videos, and listen to music.

YouTube was founded in 2005 by Chad Hurley, Steve Chen and Jawed Karim, who were all early employees of PayPal. YouTube is the leader in online video, sharing original videos worldwide through a Web experience.

Former game designers Stewart Butterfield and Caterina Fake created Flickr, an online photo sharing network, in 2004. Flickr, which began as a photo-sharing feature of their gaming project, has since then blossomed into one of the premiere photo-sharing sites on the web.

With more than 45 million users representing 150 industries around the world, LinkedIn is a fast-growing professional networking site that allows members to create business contacts, search for jobs, and find potential clients.

FriendFeed aims to be a one stop shop for all your social networking updates and news items. The four founders were all team members at Google and helped to launch such products as Google Maps, Adsense, GMail and Google Groups.

Twitter, founded by Jack Dorsey, Biz Stone, and Evan Williams in March 2006 (launched publicly in July 2006), is a social networking and micro-blogging service that allows users to post their latest updates.