Both Google's Gmail and WhatsApp announce that they have one billion users and counting. With the achievement, Gmail becomes the sixth Google service to cross one billion users, and WhatsApp becomes Facebook's second most-used app.
As of the date of the announcement, the one billion user club includes: WhatsApp, Gmail, Chrome, Facebook, Google Maps, Play Store and YouTube.
Mark Zuckerberg, CEO of Facebook said at the time of the purchase: "WhatsApp is on a path to connect 1 billion people. The services that reach that milestone are all incredibly valuable."
What makes WhatsApp popular is because its widely recognized in both the developed and developing world. Furthermore, the messaging service is also available across almost every platform and comes pre-installed on many feature phones used across the developing world, where smartphone penetration is still low.
Further reading: WhatsApp Achieves 1 Billion Users Milestone: The Work Isn't Done Yet