Talking about Google apps, the search giant's newest app to launch is Google Pay. They were designed for different purposes. The App Preview version lets you do pretty much everything the Allo app lets you do, including responding to messages and changing the size of text.
The ability to make Duo calls to people without it installed on their end should make it more accessible and reduce the complaints that "none of my friends use it".
Hangouts may or may not be discontinued which we don't know at the moment. This could be due to the app now being an Instant App or being a part of Google Play Services.
It's worth noting that the App Preview feature works only if you've added your phone number to your Google account and enabled App Preview in Settings. A user on Reddit recently spotted that his handset was showing to make a Duo call to a Nexus 6P device, even though the device did not have Duo app installed on it. Users further said that it was possible to make a call to the Nexus 6P handset.
Alongside the change to Duo, Google is improving Allo, its messaging app. Google has used App Preview Messaging since its inception to send messages to non-Allo users.
As soon as the call is made, the recipient will immediately be able to see what is being shown through the caller's camera. The app will allow them to establish a fully functioning video call and once the call ends, they will see a notification that asks them to download the program from the Google Play Store. Duo is based on phone numbers, allowing users to call someone from their contact list. Several brands of Android phones such as OnePlus come with preinstalled Duo.
Even so, this is a huge step for Duo and one that could finally make it the mainstream video calling app Android needs. It's messaging app Allo is receiving a visual upgrade as well.