JbyJ is a 4D plug-in to build a distributed system or Peer-to-Peer system using Java RMI. JbyJ provides plug-in methods to call project methods mutually between 4Ds in a network. If you use the JbyJ class library, it enables your Java programs to call project methods of 4D in a network.
Java RMI: http://java.sun.com/javase/technologies/core/basic/rmi/index.jsp
RMI is used as a communication protocol in JbyJ. Because some firewalls block this protocol, JbyJ also supports HTTP/HTTPS to pass the firewalls.
JbyJ requires JWorld, which is another 4D plug-in and distributed with JbyJ, in order to launch a Java virtual machine.