Google has Hangouts, an app which tries to integrate all of your messaging needs together including SMS and video. It can be a little confusing to use and especially as the standard Google Messenger app is also still available for SMS messages. In addition, Google also now has Duo, its new video calling app, and it seems Google has just released a series of videos to promote the app. After the relative complexity of Hangouts, Duo has a simple design and is easy to use. The promotional videos emphasize this simplicity with full screen videos shown on both Android phones and iPhones, presumably because Google are keen to show off the cross-platform functionality of Duo.
The other key feature of Duo notably demonstrated in the videos is the preview function, known as "Knock Knock". If the call recipient is using an Android phone (and the caller is an already-known contact), they automatically receive a preview video of the caller before they choose whether to answer or ignore the call. If the recipient is using an iPhone though they won't receive the preview unless they happen to already have the app open. Duo also offers full end-to-end encryption, 720p video quality and support for Google Assistant. It also has the ability to automatically switch between Wi-Fi and cellular signals as necessary to retain the call. You don't need to use your Google Account either, because Duo is based on phone numbers rather than accounts, along the lines of other messaging apps such as WhatsApp rather than the account-based system used by Skype.
Duo was originally announced at Google's I/O conference in May, along with Allo, Google's new instant messaging app that is yet to be released but is expected to arrive soon and you can currently sign up in the Google Play Store to receive notifications about the release of Allo. Duo is reported to have had more than 10 million downloads in the first month since its release and it does appear to be a big improvement over Hangouts (at least for video calling) and once Allo is released Google will hope to have a strong and popular double act in a competitive and crucial messaging app market.