CommonsWare
Mark Murphy, founder of CommonsWare, writes a lot.
Books
From 2008 through 2021, Mark wrote a series of books on Android app development. These books are now available for free download from the CommonsWare site.
His most recent books have been focused on second-generation Android app development (Kotlin and the Android Jetpack):
Elements of Android Jetpack, a new introductory book on Android app development, focused on second-generation techniques.
Exploring Android, a series of step-by-step tutorials for building an Android app from scratch. This book demonstrates app development using Kotlin, coroutines, and the Jetpack libraries.
Elements of Android Room, to help you incorporate Google's reactive object wrapper around SQLite.
Elements of Android R, to help you deal with the changes introduced by Android 11 (code-named "R"). It covers everything from scoped storage changes to data access auditing to sharing UIs between apps to bubbles.
Elements of Kotlin, a guide to the Kotlin programming language, which is rapidly gaining in popularity for Android app development.
Elements of Kotlin Coroutines, exploring Kotlin's new first-class reactive programming system.
In the beginning, Android development was focused on Java and, partially, on the Android Support Library. Mark's earliest books share that focus:
The Busy Coder's Guide to Android Development, the first and largest book on Android app programming
Things Other Than Books
He runs the jetc.dev weekly newsletter for Jetpack Compose.
Heck, he even has a blog.
All code in Stack Overflow questions, answers, or comments written by Mark Murphy are hereby licensed under the Apache Software License 2.0, unless otherwise noted where that code appears on Stack Overflow.