Distributed computing technology is really where most of the action is today. DCOM, Corba, EJB, RMI, HTTP, SOAP, XML-RPC, and Middleware Messaging are all technologies based on a simple goal: two or more applications running on different machines, coordinating to complete a task. The W3C has started a new activity to delve into the idea of using XML as a distributed computing technology. It's called XML Protocol, and it's worth checking out.
XML Protocol