Google has released Duo the video chatting app for Android and iOS. Duo doesn't require a separate account users need only their phone number to get started.
Google says it built the app to function well even across poor network connections. The app will change the resolution to match the connection speed in order to keep the call going, and can seamlessly switch from wifi to cellular.
A feature called Knock Knock gives people a preview video of the person calling so they can see what's up before answering the video call. Duo is free to download from the Google Play Store and iTunes App Store.