While it’s not exactly as great a feat as WhatsApp and Facebook crossing the one billion line, Google Play Books is only the ninth app to hit this installs mark. This app, like other Google apps, has the advantage of coming pre-installed on most Android devices. But it’s good to know that people are still looking for ways to read books on their devices. The other Google apps that have hit the one billion mark include Games, Movies, Music, and Newsstand.
Source: Android Police