Unity native plugin (iOS / Android) example / boilerplate project. Unlike many sources around the webs, this Android plugin does not touch UnityPlayerActivity. More on Unity Android Plugin Tutorial 1. Fundamentals.
To start inspect files just start with Assets/Plugins/eppz! Alert/Example/eppz! Alert Example.unity scene. Note that the iOS / Android plugin projects also included in the project root in their respective folders (Xcode project is at iOS/EPPZ_Alert_iOS, Android Studio project is at Android/EPPZ_Alert_Android).