Duo, from Google, offers one-on-one mobile video calls. (app/app)

Google’s Duo is a simple video messaging app that accomplishes the task of doing one thing very well. Think of it as Apple’s FaceTime — Google Duo is designed for one-on-one mobile video calls and nothing else. Those who use Google’s Hangouts app, which also allows for video calling, may look at Duo and miss features such as group calling. That’s a valid criticism.

Duo differentiates itself in two key ways. One, it’s tied to your phone number rather than your Google account, meaning that you don’t need a Google account to use it. Second, Duo is encrypted, so that Google itself can’t see the content of your conversations.

Despite its simplicity, Duo does have one feature that could be particularly useful for video calls on the go: If the person calling you is on your contacts list, Duo’s “Knock Knock” feature gives you a video preview of who’s on the other side. (Think of it as being able to peek through the peephole on a door.) This can be disabled, but it’s useful if you get a call and want some intel about who’s on the other side and the kind of mood they’re in. Free, for iOS and Android.

Hayley Tsukayama