HermesJMS uses Jython and has had a console since 1.10. At startup HermesJMS looks for a file called hermesrc.py in your .hermes directory to run letting you add your own extensions such as a custom message renderer or a new action.
From version 1.13 you may also set the system property hermes.python.url to reference some code on a webserver somewhere. This is especially useful with webstart as it allows different Hermes jnlp files to have different localisation.
As a Java programmer I'd recommend that for any substantial extensions to Hermes you use Java and think of python as the glue code to bind your functionality into Hermes.
If you have any questions or want to share your python scripts then use the python forum. The Hermes javadoc is here.
The Hermes Messaging Model
In the core of HermesJMS is a helper library for JMS that uses the configuration XML to create and manage JMS connections, sessions, producers and consumers. It basically does all the boring JMS work and hides it all behind a simple facade - the Hermes interface. The GUI is then built using this framework.
If you intend to extend Hermes via python then read more on the Hermes Messaging Model
Some Common Examples