JDOM2 is being 'released' as snapshots containing the state of the code at that given date/time. The timing of these snapshots is irregular, but, whenerver a snapshot is released, you can assume the following:
These snapshots are available on the Downloads page.
When JDOM2 'final' is released, the official version will be on www.jdom.org
The snapshot is named based on the time the snapshot was compiled - jdom-2.x-yyyy.mm.dd.HH.MM.zip. The 2.x indicates that it is a snapshot, and the remaining numbers are the formatted date, hour, and minute of the snapshot (Eastern Time - Canada).
The snapshot contains the compiled JDOM 2.x jar, as well as the contrib and test code jars (compiled). Additionaly there is the complete source code (for the core JDOM as well as the Unit tests, and contrib code - not in the same structures as the Git repository, but structured to be usable by Java IDE's like eclipse - to be able to step-through the code in a debugger, for example). Finally there is a jar containing the API documentation for that snapshot release.
In addition to the JDOM code, source, and apidoc jars in the zip file, there are also the jaxen and xerces jars needed to complete the 'runtime' code. If you want to do a full load of the code in to an IDE and do more than just 'use' JDOM you will also need the development/comile jars which are needed to support the Ant build process. Get those jars here