The latest Microsoft app tom hit the 100 million install mark on the Google Play Store is Outlook, as was spotted by MSPU over the weekend. It joins apps like Word, Excel, PowerPoint, OneDrive, Skype, OneNote, and SwiftKey in the club. Those apps have many more installations though, as Word, Excel, PowerPoint, Skype, and OneDrive all have over a billion installations, while OneNote and SwiftKey have 500 million.
Microsoft's Frank X. Shaw noted back in April that Outlook has 100 million users on iOS and Android. However, that's counting users, while the Google Play Store is counting installations. It's also worth noting that the Google Play Store doesn't account for all Android devices. Amazon offers Outlook on its own app store, as do other vendors.
The next milestone for Outlook to hit in the Google Play Store will be 500 million, since Google doesn't count anything in-between that and 100 million. Microsoft is always continuing to improve the product, as well as making deals with OEMs to get Outlook preinstalled. Naturally, it will also be preinstalled by default on the upcoming Android-powered Surface Duo.