One of Allo's highlight features is Smart Reply, where the app guesses what you might respond to a message with, and adds a button to send that response. A few other apps have implemented it as well, like Android Messages, but usually not in notifications. Google seems to be testing an app called 'Reply,' which adds smart replies to other messaging apps.

Invites to test Reply were sent out by Area 120, a division of Google that works on experimental products. Here's an explanation of the app, from the email sent out to testers:

You probably get a lot of chat messages. And you want to be there for people, but also for people in the real world. What if replying were literally one tap away? Reply puts the Smart Reply you may know from Google right into notifications from the chat apps you use most often. It looks like this: But it also adds replies that are slightly smarter, like this: Other things to try: Do Not Disturb. When you’re driving, Reply can silence your phone and tell people who message you that you can’t chat right now

When you’re driving, Reply can silence your phone and tell people who message you that you can’t chat right now Don’t miss the important stuff. When you get an urgent message like “We’re waiting for you!” Reply can make sure to get your attention even when your phone is silent.

When you get an urgent message like “We’re waiting for you!” Reply can make sure to get your attention even when your phone is silent. Vacation responder. Reply can check your calendar and tell people if you’re not working.

Reply can check your calendar and tell people if you’re not working. Your Favorite Chat Apps: Reply works with Hangouts, Allo, Whatsapp, Facebook Messenger, Android Messages, Skype, Twitter DMs, and Slack.

At least part of Reply's functionality may be coming from Gboard, as a recent teardown revealed that an identical feature was in development. Perhaps the Reply app activates some functionality in Gboard, or the app is for people who use another keyboard.

If you want to sign up for details, the email links to this form, which you can fill out to receive more information. The app hasn't actually been sent out to anyone, so we don't have an APK quite yet.