Tap It! is a simple tapping Android game that demonstrates Google Sign-In and the Play Games Services (Achievements and Leaderboards).
To make the app run modify the file games-ids.xml (in app/src/main/res/values/) following the instructions provided there.
Afterwards, create your own "google-services.json" configuration file from the second step of this page: Sign-In for Android and copy it to the /app folder.
The last version of the app can be downloaded for free from: Tap It!
My other apps can also be downloaded from: CyclOps Development apps.
If you need help running or modifying the app, send me an email.