Google has killed so many applications that I saw "Duo" in my app list and accidentally thought it was the name of the many chat apps Google has had, so I deleted it. I realized that it was my mobile authenticator and tried to reinstall it, but my phone was too old for the version on the Play store. Luckily, Duo provides the APK for older releases so I was able to side load it.
Basically, Google's caviler attitude with cancelling services almost locked me out of all my accounts. Thanks Google.