The best part about Duo calling app is, it is very easy and simple to use. Just like iOS Facetime app, all you need is a phone number and you will be able to call other numbers in your contact list. After an easy signup step, you can call with one tap.
The most interesting feature of the app is “knock knock” which lets you see the video of the caller before you decide to answer the call or ignore it. All Duo calls are end to end encrypted making it a secure conversation.
The release of this app comes in at a very interesting time, Google recently announced its shutting down of Google + Hangouts on Air on September 12.
The app will be available worldwide in few days.