Guava is a suite of core and expanded libraries that include

Meta modelling framework to write cutting-edge annotation processors

Stuff related to immutable object trees, including parboiled as and transformers.

Elegant parsing in Java and Scala - lightweight, easy-to-use, powerful

Annotations the SpotBugs tool supports

Compile time annotations and compile time annotation processor to generate consistent value object using

Simple, but superior to others, META-INF/service file generator

Testing dependencies and utilities. Expected to be used only in test scope