My personal project (no longer listed in the App Store because I didn't feel like paying for the Google Places API / updating it) was an app that would get your current location, and then show you places to eat around you one at a time with a brief description, and linked out to the system Maps app to give directions. Built entirely in Java.
This app was the first app in Android I had ever touched. It has a suite of built in Unity games and has coupons to local businesses for playing the games.
Had a major role in building the skeleton of the Android version of this app before handing it off to another developer for the finish line.
Implemented several native plugins that interacted with the core Ionic app in Kotlin. Such as: storage (with Room DB), custom camera, biometric authentication, etc.