Sundar Pichai in a tweet announced that Google’s new video calling app, Duo had over 5 million Android downloads in a week. Google Duo was initially publicised alongside a chat app, Allo back at the Google I/O in May . Google Duo started rolling out to devices on 16 August. We guess Pichai is discounting the first couple of days after the launch in the count. https://twitter.com/sundarpichai/status/768657715962839041 Duo is by far one of the simplest video calling apps around . The most critical functionality, of making and accepting calls is just a tap away. There is a knock-knock feature that shows you footage of the incoming call before you accept it, allowing users to get an idea of what to expect before answering. Duo is a one to one application, to reduce complications, and is end to end encrypted. The application has been engineered to work seamlessly on a wide range of connectivity scenarios. It is possible to seamlessly transition from Wi-Fi to cellular connectivity while still maintaining a connection through the app. Google’s Amit Fulay, Google Duo’s project lead, has said that a voice-only version of the app is on its way. The app has been popular in an overcrowded market, and reached the top of the trending charts in the Play Store. Here is how Duo compares with other popular video calling apps.