Version 5.0.0.GA is built on top of the new JBoss Microcontainer, which replaces the JMX Microkernel of the 3.x and 4.x JBoss series. It also integrates well with the JBoss framework for Aspect Oriented Programming (AOP). JBoss 5 is designed around the notion of a Virtual Deployment Framework (VDF).

Key features of JBoss 5 come from the integration of other standalone JBoss projects. Highlights include:

• The addition of JBoss EJB3. EJB3 focuses on simplifying development, enabling a test driven approach, and writing plain old Java objects rather than coding against complex EJB APIs.
• The incorporation of JBoss Messaging. This high performance messaging service provider is in the JBoss Enterprise Middleware Stack. It replaces JBoss MQ from the JBoss AS 4.x series.
• The introduction of JBossCache. It is available in two forms, the traditional tree-structured node-based cache or PojoCache.
• The addition of JBossWS. This Web services stack includes JAX-WS-2.0.
• The addition of JBoss Transactions. This transaction manager is one of the most interoperable implementations available.
• The incorporation of JBoss Web. This Web container is based on Apache Tomcat and includes the Apache Portable Runtime and Tomcat technologies.

The release also contains a multitude of bug fixes.  Among them:

• A fix was applied to a NullPointerException in WebServiceDeployerEJB.
• A repair was made to a NullPointerException in the expiration of passivated sessions.
• A correction was made to a NullPointerException for JavaServer Faces managed beans.
• The bootstrap dependencies failure of EJB3 session beans was fixed.
• The deployment failure of @WebService was resolved.

Along with the long list of bug fixes and enhancements, several compatibility and configuration issues are addressed in the release notes found here.

Note: The JDK 5 compiled JBoss binary is the JBoss development team's recommended binary version. While the JBoss 5.0.0.GA can be compiled from source using either JDK 5 or 6, the binary compiled under JDK 6 requires additional manual setup and has some known issues.
The JDK 6 JBoss provided below removes the need for manual setup, but does not address the known issues. Please see the release notes for information on the outstanding issues with JDK 6.