4. Instagram

Originator(s): Kevin Systrom and Mike Krieger

Year: 2010

Worth: $ 1,000,000,000 (as per Facebook’s announcement of acquisition)

How it took off: A free photo-sharing program isn’t a bad place to start either. Kevin and Mike put their heads together to let photos get shared in a way that wouldn’t annoy those it was shared with. Users were able to see other’s pictures, follow photographers, and post their own artistic-looking photos with the help of digital filters. The photos were made to resemble the Kodak and Polaroid square-shaped pictures, and so struck a chord with the legacy of photography as well. Although Kevin and Mike had no plans to sell the site, Zuckerberg made an irresistible offer of $1 billion, and Facebook on April 9, 2012, announced that it would acquire the company, along with its 13 employees.

5. Quora

Originator(s): Adam D'Angelo and Charlie Cheever

Year: 2009

Worth: $86 million (as of 2010, according to data from gigaOm.com)

How it took off: Two ex-Facebook engineers (Adam was Facebook’s CTO and Charlie was its head of engineering) created Quora, a Q&A website that sought to answer questions  in a way that gave quality of experience. Adam reportedly was inspired to create Quora when he thought ‘that Q & A is one of those areas on the internet where there are a lot of sites, but no one had come along and built something that was really good yet’. It has been in SiliconValley media especially since it features questions about startups and entrepreneurship (it even attracted senior Silicon Valley executives who answered questions about their experiences). It is organized and edited by its community of users, so answers are relevant to those who post questions.