chess4j is a chess program written mostly in Java, with a little Groovy used in some I/O type functions. The goal of chess4j (besides just having fun) is to serve as a test bed for various interests, including parallel and distributed computing, machine learning, and exploring different JVM languages and technologies. There have been three major releases. I write about the development of chess4j in my blog under the chess4j category.
chess4j-3.0 released Jan. 2016
chess4j-2.0 released June 2014
chess4j-1.2 released Feb. 2013
chess4j is distributed under the MIT license. See LICENSE.TXT in the download for details, but essentially it means you can do pretty much anything you want with chess4j as long as (1) you don’t hold me liable, and (2) you provide attribution back to me.
You can also download the source code from the project website on Sourceforge.