Netifera is a very interesting 100% Java-based Open Source network security platform. The next version will include a probe, which is a "deployable software agent that makes it possible to run all netifera platform tools remotely".
The probe uses JamVM and a cut-down version of GNU Classpath. This is downloaded onto the remote site to run the netifera tools. My thanks to Claudio Castiglia (of Netifera) for sending me the following link to a webcast showing the probe in action:
JamVM and GNU Classpath are mentioned starting 14:54 into the webcast in the discussion of the probe architecture.