2. Snapchat

Snapchat debuted in the App Store in the summer of 2011 as a messaging app for sending disappearing photos. At the time, it was called Pictaboo, but it had the same now-famous ghost icon, Ghostface Chillah.

By September 2011, the name had changed to Snapchat and the app began to catch on with teens.

Six years later, Snapchat is owned by a $22 billion public company, Snap Inc., and has expanded into TV-like shows, partnerships with publishers, hardware products, and augmented reality.