In this download area, you will be able to download the distribution (binary and source), the Windows installer (for some of the versions) and the documentation for Groovy. You may also be interested in third-party packages, such as the Ubuntu-based PPA packages.
Groovy 2.1 will be the next major version of Groovy
You can have a look at the JIRA release notes
Groovy 2.0 is the new official major version of Groovy.