You can download the latest code for xjava from
http://xjava.googlecode.com in the SVN repository.
Though it might be a good idea to add the functionality to have return values be used in WorkUnits, by default there is no return value expected from them. If you need something returned the unit itself should call off to set it, and if you want to wait for the work to complete or check on its status you can get the return from addWork that is a Future to let you know when it's finished.
Most of the intent behind ThreadManager is to handle asynchronous tasks that have no necessary response of their own but simply need to do something. This is sort of like the SwingUtilities.invokeLater concept.