What is Google Duo?
Google Duo provides simplified ‘one tap’ video calling on Android and Apple iOS platforms, and the ability to work better on low bandwidth connections.

The application, which is being rolled out worldwide over the next few days, will compete with Microsoft’s Skype and Apple’s FaceTime.

Distinct Features
1.  A distinct feature on the app — Knock Knock — allows people to see live video of a caller who is in their phone book, before answering. Early reviewers said this would help people look presentable before taking a call. The feature can be disabled totally, or callers blocked. 

2.  Also, for video calls on the go, Duo switches between Wi-Fi and cellular data seamlessly, without dropping the call.

3.  Duo has been built with an emphasis on privacy and security, and all calls are end-to-end encrypted, the company said.

4.  Call quality adjusts to changing network conditions to keep one connected – when bandwidth is limited, Duo will gracefully reduce the resolution to keep the call going smoothly.