What is it?

In a nutshell it's a natural next step, building further on object-oriented programming (OOP), where objects become active talkative peers.

Imagine running thousands of concurrent programs on one computer where each program instance represents something or someone in the real world. Some things are passive and only react to events but lots of real world things also take initiative.

That's why parts of this kind of system can better be represented in software by "autonomous agents" or "actors" which frequently interact with each other.

Groovy?

The Groovy language, which could be called the second language on the JVM after Java itself, removes most of the syntactic noise that gets in the way of programming actors in Java, and gives us new tools and techniques that we can leverage to tidy up the code.

Groovy Actors leverages the seamless integration of Groovy and Java to create a platform for building large populations of interacting active objects.