While working at Facebook in 2009, Adam D'Angelo and Charlie Cheever had a question: Why isn't there a place on the Internet where a question can be answered by someone who actually knows the answer?

That question led the pair to start Quora, a Q&A website that allows users to share knowledge. You can pose a question, answer a question, and edit others' answers. The concept wasn't exactly new, but D'Angelo and Cheever knew exactly what would make Quora unique: quality.

"It was an area of the Web that hadn't been developed or done well yet," says the mild-mannered D'Angelo, who was Facebook's CTO and VP of Engineering at the time. "It was like the state of search before Google or the state of social networking before Facebook. There were plenty of Q&A sites out there, but we wanted to do it better than anyone else."

Leaving Facebook behind, the duo started building Quora in April 2009. By June, they had hired their first employee, Rebekah Cox, to work on the design of the site. Like many other start-ups, the ambitious team didn't have a traditional business plan. 

"We iterated on the product for months before we decided what it was going to be," D'Angelo says.  The team tried out ideas until the finished product was acceptable to everyone.

The start-up received $11 million in first round funding from Benchmark Capital's Matt Cohler, a former Facebook executive who then took a seat on the company's board, according to a recent Fast Company story.

In June 2010, Quora officially launched and it became wildly popular among the tech crowd. From the beginning, the answers consistently (and surprisingly) contained quality information. For example, a Quora user asked "What does Dustin Moskovitz think of The Social Network?" The answer came from Facebook co-founder Dustin Moskovitz, who said the movie was an "interesting" portrayal of what really happened. It was that kind of star power that soon attracted the mainstream.

Another distinctive feature is Quora's interface, which is similar to other social media platforms. Users sign up and can follow feeds that contain questions and answers on different topics, like science or food. A user's homepage is an aggregated list of all the most recent activity in those chosen feeds.

"It got intense immediately after we launched, because tons of people started using it everyday," says D'Angelo. "There was so many things to do, we couldn’t go at our own pace anymore."

But the two founders are notoriously quiet about Quora's revenue model. At a TechCruch Disrupt conference in May, Cheever gave a hint to a possible strategy. He was asked in an interview if Quora would "probably" be looking at an advertising model in the future.

"Your hunch is right," Cheever said. "We are just really focused right now on building out the product, and getting a good set of question and answers."