Groovy 1.0 is the latest stable release.
Once you've download the distribution, please read the installation instructions.
Groovy 1.1-beta-2 is the latest packaged preview of the next version of Groovy. Visit the Roadmap to find out further details.
Other ways to get Groovy
You may download other distributions of Groovy from this site.
If you prefer to live on the bleeding edge, you can also grab the source code from SVN.
If you wish to embed Groovy in your application, you may just prefer to point to your favourite maven repositories or the codehaus snapshot maven repository.
If you are an IDE user, you can just grab the latest IDE plugin and follow the plugin installation instructions.