Barely four days after its rollout, Google’s new video calling app is topping the charts for free apps for Android on Google’s Play Store. Justin Uberti, the app's technical lead, tweeted on Friday that Duo became the top free app. Uberti also announced that the rollout of the app is now complete, and Google Duo should now be available in all countries for free download, NDTV's Gadgets 360 reported. The app's key feature is that you can see a live video feed of who is calling you even before you pick up the call.

The app tops the lists of 'Top New Free', and 'Trending' sections on the Play Store, higher even than Nintendo's wildly popular Pokemon GO. In the India App Store, Google Duo is the most popular under the free section, with WhatsApp, ShareIt, and Facebook trailing far behind. It also sits on the top spot for free apps in the United States Google Play story, above other popular apps such as Facebook, Facebook Messenger, Instagram and YouTube Music. In India, the app sits on the sixth position with WhatsApp, Facebook Messenger, ShareIt, Facebook, and UC Browser apps still in the lead.

The app was first announced at the I/O developers conference in May, where the tech giant promised a global rollout in a few months. Initially, a few users in US and Canada complained about failed verification via SMS, which was soon rectified. Google Duo, which many consider as Google's answer to Apple's FaceTime calling service, is gaining traction on Apple devices as well. It ranked No 22 among all free apps and No 4 in the free social-networking app category, according to AppShopper.