When it comes to social networking, it's wise to put your best face forward. Facebook, the social networking juggernaut, lets users share information, post photos and videos, play games, and otherwise connect with one another through online profiles. The site, which allows outside developers to build apps that integrate with Facebook, boasts more than a billion total users. The firm was launched in 2004 by Harvard student Mark Zuckerberg as an online version of the Harvard Facebook. (The name comes from books of freshmen's faces, majors, and hometowns that are distributed to students.) In 2012 Facebook began publicly trading after filing one of the largest IPOs in US history.