At Google I/O 2016, Google announced two new and separate communication apps: Allo, a new instant messenger app, and Duo a video calling app. Today Google announced Duo is finally rolling out to the masses on Android and iOS.

Google Duo is a video calling app and just a video calling app—it does one-to-one video calls and nothing else. It's also only available for mobile phones—there are no Web, Chrome, or desktop clients. It doesn't even require a Google Account—Google says that "all you need is your phone number and you’ll be able to reach people in your phone’s contacts list."

Duo has two features. The first is that the video calling is claimed to be "fast and reliable" even with limited bandwidth. It can switch between Wi-Fi and cellular data without dropping the call and can "gracefully degrade" the video when bandwidth gets low. The other feature is called "Knock Knock," which shows live video from your contact on the incoming call screen before you even answer the call. Knock Knock doesn't work on iOS right now. On the security side of things, Google notes that "all Duo calls are end-to-end encrypted."

What about the billion+ users of Hangouts?

Google's other video calling app (and instant messaging app), Google Hangouts, isn't going away. With the advent of Duo and Allo, Google has maintained that Hangouts will be transitioning to an "enterprise" product. Google hasn't talked about what will happen to the existing users of Google Hangouts, however.

When Google made the transition from Google Talk to Google Hangouts, Hangouts was an in-place upgrade to the Google Talk Android client. Just look at the URL of Google Hangouts on the Play Store: https://play.google.com/store/apps/details?id=com.google.android.talk. Hangouts took over the Google Talk package name—"com.google.android.talk"—so everyone that was on Google Talk got automatically upgraded to Hangouts.

Google Talk/Hangouts has been Google's default instant messenger since Android 1.5—that's six years of user accumulation by being a default app. According to the Google Play Store, Hangouts has over a billion users. Allo and Duo have their own package names, which means Hangouts users won't be upgraded to them, and Google has yet to reveal a plan to upgrade the billion+ users of Hangouts. It also hasn't said whether Allo and Duo will become default apps on Android.

The Duo/Allo plan didn't make a ton of sense when it was announced, and it doesn't make a ton of sense now. Hangouts works on Android, iOS, Chrome OS, the Web, and through Chrome extensions, on Windows, macOS, and Linux. It supports one-to-one video calling and group video calling, along with video overlays and effects. Hangouts supports instant messaging and SMS and integrates with Google Voice and Project Fi. Hangouts is generally neglected and mismanaged, but pushing users away from Hangouts and toward a less fully featured product doesn't feel like a good answer. Forget about the rest of the world, Google has a lot of work to do if it even wants to win its own users over.

The rollout for Duo starts today, and it will be available worldwide "in the next few days."