JGroups is a toolkit for reliable multicast communication.
(Note that this doesn't necessarily mean IP Multicast,
JGroups can also use transports such as TCP).
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
* 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)

WWW: http://www.jgroups.org/