“Google Duo is a free video and audio calling app made by Google. Duo relies on your phone number, enables you to reach people in your phone’s contacts list, offers end-to-end encryption, and has nifty features like Knock Knock, which allows you see live video of your caller before you answer.”– Pocket-lint
why Google Duo?
Duo is unlike other video calling services in that it is extremely straightforward and easy to use. All you need to do is sign in to the app, select a contact you wish to call, and tap the video call button. The interface is as minimal as it gets; you just see a list of contacts that have Duo installed, and there’s the option of inviting your friends over for those that don’t already use Duo.