Facebook at 21
I saw that today is the anniversary of the start of Facebook back in its undergraduate days of 2004. An old post on the now-defunct Writer's Almanac did a nice job of summarizing that early history, so I am using most of it here.
The social networking site Facebook was launched from a Harvard University dorm room on February 4, 2004 by sophomore Mark Zuckerberg in his dorm room (Suite H33 in Kirkland House). He was aided by three other 19-year-olds.
Zuckerberg was a smart, middle-class kid from Dobbs Ferry, New York who started writing computer software when he was 12. In high school, he created a program called Synapse Media Player and was offered millions of dollars for the product and job offers by both Microsoft and AO. But he passed on them in order to attend Harvard instead.

The program he created at Harvard was called Facemash. It displayed two student photos side by side and asked people to rank who was hotter. It would later be duplicated in various forms as a "hot or not" game. In the site’s first four hours online, the photos were viewed 22,000 times. The site was shut down by Harvard a few days later. It so popular that it overwhelmed their server, but also because there were privacy violations since Zuckerberg had acquired the photos for Facemash by hacking into Harvard’s photo directory.
A couple of months later, Zuckerberg began writing code for a site that would allow students to view each other’s photos and some basic personal information. This site, TheFacebook, was launched on this day in 2004 at www.thefacebook.com.
More than a thousand students signed up within 24 hours, and after a month, half of Harvard’s undergraduates had signed up. Zuck was in trouble again, this time with three seniors who claimed that they had hired Zuckerberg to create a similar site, but that Mark had stolen their idea. Several years later, they reached a multimillion-dollar settlement.