I have recently published Crypto Ledger on Google Play.
The app is an extension of the Crypto Ledger website. It makes use of the Crypto Ledger API to buy, sell, and monitor coins.
The Crypto Ledger app was built using Kotlin and Android Studio. It uses coroutines and retrofit to make API calls, and fragments for navigation.
Buying and selling coins requires an API Key, while getting live price data does not.
The source code is available on GitHub: https://github.com/TMDStudios/crypto_ledger_app_kotlin
You can see the website here: http://crypto-ledger.herokuapp.com/
The website repository is available here: https://github.com/TMDStudios/crypto_ledger
You can also read more about the Crypto Ledger project here: https://www.publish0x.com/open-source-projects?a=oQeZVWD6ep&tid=GitHub