Looking at your post's timestamp, on the 5th of December you were asking right before the release of JBoss Application Server 6.0.0 on the 28th. In that time the AS6 range has progressed past the 6.1.0.Final release cycle, while AS7 has undertaken a rapid development cycle.
At the time of posting, you can download JBoss Application Server 7.0.2.Final, as well as 7.1.0.Beta1b, depending on how close to the cutting edge you would like to be. To make sense of the version codes and some of the software release life cycle:
- Final = a polished, tested, and approved version
- GA = General Availability, a final version preparing for the big time
- CR = a Candidate Release in the running for GA, undergoing final testing and QE
- M = a Milestone release, rolling features and bug fixes into a build
- ER = an Engineering Release, typically a build for the engineering team
All of these will differ from organisation to organisation, as the profiles for what each Milestone Release represent are subject to the flavour of project management. As an example, look at the Meego Wiki page for the explanation of their Milestone releases.