Flock is a free web browser. Built on Mozilla's Firefox, Flock enables you to instantly upload photos, share photos and videos by drag-n-drop, blog, and get notified when your friends update profiles on social media sites like Facebook, Twitter, Flickr and YouTube. Flock is a free alternative to Internet Explorer and other Internet browsers.
Elgg empowers individuals, groups, and institutions to create their own fully-featured social network. Similar in some ways to diigo.com, it allows people to create an online community. It even has a social bookmarking facility.