There is an interesting, open-source ebXML MSH available at http://www.freebxml.org/msh.htm It has only been available since September so I'm not sure how good it is. Has anybody out there used it yet?
I've used it. I think this one might take off. But I'd like to see a JMX type of messageing system. Not sure if the freebxml one could be worked into an MBean. In fact it might not be possible due to the fact that you need to use http posts....therefore that means servlet engine.
I currently work for a company that is going to start testing emXML messaging within the next couple of months and we will be using Jboss as the app server.