I heard of something cool for the first time today it work: a Java messaging system called JavaGroups. From their website, answering the question "What is JavaGroups?::

JavaGroups is a toolkit for reliable multicast communication. It can be used to create groups of processes whose members can send messages to each other. The main features include

• Group creation and deletion. Groups members can be spread across LANs or WANs
• Joining and leaving of groups
• Membership detection and notification about joined/left/crashed members
• Detection and removal of crashed members
• Sending and receiving of member-to-group messages (point-to-multipoint)
• Sending and receiving of member-to-member messages (point-to-point)

We're looking around for message queue type middleware, and leaning towards freeware/open source systems without restrictive licenses. This one is LGPL and looks good so far. Of course, all these things always look good in the overview pages.