Android

General Pages

android.com, with phones and links.
Android on Wikipedia, clearly a popular topic.

Android Development

These are resource you'd care about the most as an application developer.

Android API Reference
Jetpack Reference
NDK Reference
Android Developer page.
Android Developers Blog, announcements and a little bit of everything.
Android on GitHub has many repositories and projects for LLVM and NDKs.

AOSP Development

These are resources you'd care about the most if you were building for a new device.

Code Search
Android Open Source Project homepage, or AOSP for short.
Architecture
Graphics has a lot of information but given how I care about this kind of stuff, you should expect to see me add more things.

Languages

Java and Kotlin are the two main managed languages. C/C++ is also used in various places, of course, and more recently Rust.

Java 8 support on Android (hello lambdas!)
Java versions in Android builds is a bit of a mess, honestly.
JNI spec, the Java Native Interface.
Kotlin docs
Kotlin on Android

Graphics

Graphics documentation center on AOSP.
Android Graphics Shading Language for use with RuntimeShader.
OpenGL ES, an old classic.

Posts

My Android posts include a few that I reference regularly.