Back in May of this year, Google’s video chat app Duo reached 500 million installations. Six months later the app has reached the billion-download mark. This comes both from people who installed the app as well as those that get the app pre-installed on its phones. Duo launched around the same time as Allo, the latter wasn’t quite as successful as the former. Allo will be shutting down in March 2019. 

Source: Phone Arena