The tool is part of the Enterprise Manager, which is included when you purchase a support subscription for Sun GlassFish Enterprise Server v2.1. For more details on the Enterprise Manager look here. For more details on the Sun GlassFish Portfolio subscription plans, look here.
Here are two screenshots, which should ring a bell if you're a Java VisualVM user or a NetBeans Platform developer:
Three cheers for this new NetBeans Platform application. It should be added to the NetBeans Platform Screenshots page soon.
For all the details on the tool, go here in Shreedhar's blog.