Duo by Google lets you make simple person-to-person video calls, across Android and iOS.
Easy to set up and use: After you download Google Duo, verify your phone number and approve a few permission requests, and then you're good to go. Duo's interface is easy to navigate: Tap the Video call button to ring someone up, and tap to accept a call from a friend.
Uses your phone number: The app is based on your phone number and lets you call anyone in your contacts list who is also using Duo. Likewise, anyone with your number can contact you if you are both using the app.
Make a call: When you click the Video call button, you see a list of friends who are running the app. If you want to call someone who doesn't yet have the app, find them in your friends list and click Invite to send them a link to the app. You also see recently called friends in the app's main window. Once you're in a call, you can mute your mic, swap between front and back cameras to change what your caller sees, tap your image in the bottom-left corner to make it swap places with your caller's image, and choose whether to use an internal or external mic.
Secure and efficient: Google says Duo calls are end-to-end encrypted. Duo attempts to save data by connecting first to a Wi-Fi network to make the call. If it needs to use your mobile network, it lowers your connection rate to conserve data.
Who's there: When someone is trying to reach you, the app uses a feature called Knock Knock that can display a live video preview of the caller, which lets you see who's on the other end and perhaps the nature of the call. You can accept or decline the call. If you miss a call, you'll receive a notification about who tried to reach you.
Crowded field: While Duo is simple to use, it enters an already crowded room of mobile video-calling apps, including iOS's FaceTime and Facebook's Messenger. Some of those calling apps offer more capabilities, such as group calls or voice-only calling.
Google's Duo video-calling app does one thing extremely well: It lets you easily chat with any friend in your contacts, whether they are on Android or iOS.