Facebook Messenger has reached the impressive milestone of one billion users this month. Five years after its launch, the app has become just the third mobile app to reach the number, after WhatsApp and YouTube. With 17 billion photos and 22 million GIFs sent on the service each month, Facebook Messenger also has 18,000 bots currently on the platform, with 23,000 developers signed up to its wit.ai bot engine. The app originally came about as a way to improve group chat on Facebook's site and on mobile, before it was removed and developed into its own app. Facebook's current head of Messenger, David Marcus, believes that due to that fact that users “don't need a phone number but you can find each other by name”, it is becoming “an important communication tool for the world”.