For being the WhatsApp of images.
With 130 million uniques each month, Imgur, a trove for viral memes and photos, is now one of the Internet's most-visited sites. After seeing a social network bloom, Alan Schaaf and his team have added features such as comments and private messaging, along with galleries of its most popular images. This year, the company raised $40 million in a round of funding. "People come home from work and they just want to unwind," Schaaf says. "[On Imgur,] they don't need to log in, they don't need to create an account, they don't need to pick interests. They just hit the next button."