It is a Simple Moon Phase Calendar. There is also a widget. It is the succeeding app that renewed "Simple Moon Phase Widget". Improved point: Upgraded calendar Lightweighting of app capacity. Notification is possible without setting the widget to the home screen.
Fxwill is the official developer of Simple Moon Phase Calendar that can be found in the Weather category. The latest update of this application was launched on Oct 1, 2019 and the tool has been installed by over 100K users. Users rated the app 4.3 on Google Play.