Overview (Groovy 2.4.16)

Packages
Package	Description
groovy.mock.interceptor
groovy.test
groovy.transform
groovy.util	Various Groovy utilities for working with nodes, builders, logging, JUnit test cases, text expressions, Ant tasks or JMX MBeans.
org.codehaus.groovy.runtime	Runtime classes for Groovy - whether the dynamic interpreter is being used, the compiler or the bytecode generator.
org.codehaus.groovy.transform

Groovy - An agile dynamic language for the Java Platform
(JavaDoc for Java classes)

Groovy...

is an agile and dynamic language for the Java Virtual Machine
builds upon the strengths of Java but has additional power features inspired by languages like Python, Ruby and Smalltalk
makes modern programming features available to Java developers with almost-zero learning curve
supports Domain-Specific Languages and other compact syntax so your code becomes easy to read and maintain
makes writing shell and build scripts easy with its powerful processing primitives, OO abilities and an Ant DSL
increases developer productivity by reducing scaffolding code when developing web, GUI, database or console applications
simplifies testing by supporting unit testing and mocking out-of-the-box
seamlessly integrates with all existing Java objects and libraries
compiles straight to Java bytecode so you can use it anywhere you can use Java