Facebook is a popular social-networking service. Originally offered to college students, it later opened up its doors to anyone with an e-mail address.
Facebook gives users a place to make and explore personal profiles and interact with friends. While offerings were initially limited to a comment board called "The Wall" and a personal picture, the site now has several in-house services like user chat, photo hosting, interest groups, status messages, link sharing, and the news feed.
Facebook's biggest move, however, was introducing a development platform that lets developers make their own applications for Facebook. These applications can run the gamut, from single-use widgets to full-blown Web sites that can be accessed and integrated into a Facebook user's data. Users can add as many applications as they want, then integrate and rearrange them on their profile page.