Topic: Java and XML, P2P Java, Open Source Java
Juxtapose (JXTA) was originally one of Bill Joy's research projects aimed at developing a network programming and computing platform able to solve a number of the problems in modern distributed computing. JXTA has since become a community-based open source development platform. The four main concepts of the JXTA project are: the ability to "pipe" from one peer to another, a grouping notion, the ability to monitor and meter, and a security layer.
The JXTA Shell is a prototype application that illustrates the use of JXTA Technology. The JXTA Shell permits interactive access to the JXTA platform's building blocks through a simple, text based interface (available on Solaris Operating Environment, Linux, or Microsoft Windows).
A Technical Specification provides a description of the architecture and key elements of the Project JXTA technology including: peers, advertisements, messages, pipes and protocols. Demonstrations are available for download. See the FAQ or the documentation page for more details.
Check out OpenP2P.com's Project JXTA Developer Contest.