Facebook

Facebook launched in 2004 as a Harvard-only site. It slowly expanded to welcome people with .edu accounts from a variety of different universities. In mid-2005, Facebook opened its doors to high school students, but it wasn't that easy to get an account because you needed to be invited. As a result, those who were in college tended to invite those high school students that they liked. Facebook was strongly framed as the "cool" thing that college students did. So, if you want to go to college (and particularly a top college), you wanted to get on Facebook badly. Even before high school networks were possible, the moment seniors were accepted to a college, they started hounding the college sysadmins for their .edu account. The message was clear: college was about Facebook.
Viewing American class divisions through Facebook and MySpace