Google Duo is a new video calling app for iOS and Android, a companion app to Allo.

Google has officially announced Duo, a new video calling app that will work for both Android and iOS devices, allowing for steady streams of the content even on a poor connection. It will also feature a brand new feature called “Knock, Knock,” which will offer a live video stream of the person calling you — before you answer the call.

Duo’s video calls offer end-to-end encryption as well, and has a flurry of enhancements behind-the-scenes to make the calls instant and smooth.

Duo proactively works a network’s quality multiple times a second, and will degrade smoothly if a connection worsens. And it will automatically switch to a better connection if one becomes available. Video and audio is streamed in high-definition as well.

Duo will be available this summer, probably for free, for both Android and iOS.