JXTA's an extremely ambitious project with a steep learning curve. A quote from the column:
The formulation of networks on the fly, with or without a central server, through firewalls and with authentication and encryption, atop the Internet and other networks -- just writing a spec for a project like that is enough to inspire shock and awe. But JXTA offers all that and more.
Note the absence of the word "Java" from the description of the project -- the language is used for the reference implementation of the protocols, but JXTA is intended to be language independent.