Also from Dan Creswell, a new release of Blitz Javaspaces is nearly available.
If you are not familiar with Javaspaces you will want to understand the programming model. (Among other resources, Dan's.)
Javaspaces is the most dynamic Java programming mechanism I know of. If you have a need to use Java but you like dynamic language things like Smalltalk, and dynamic concurrency and distribution like Erlang, you may like the Javaspaces programming model.
If you like object-oriented databases (for some strange reason), then Javaspaces gives you 80% of those benefits at 20% of the pain, suffering, and risk. No one really needs that other 20% of the OODB benefits anyway. Some kind of a database is typically involved in a complete system using Javaspaces, but it plays much less of a central role in the goings on.