ulxmlrpcpp is a library to perform calls via XML-RPC in an object oriented approach. It is possible to create both client and server applications in multithreaded environments. Unlike other implementations, it does not insist on HTTP for transportation, but might also accept other ways (e.g. a simple serial line with a user-defined protocol). For HTTP as a transportation protocol, the following features are supported: cookies, SSL/TLS, proxy, SSL/TLS over a proxy, and chunked transfers. ulxmlrpcpp is also able to transmit data faster with binary XML.
OpenEJB is a simple, lightweight Enterprise JavaBeans (EJB) container and server. You can embed OpenEJB in your own applications, or in a Web application server like Tomcat, or run it as a standalone EJB server. It supports EJB 3.0, 2.1, 2.0, and 1.1, and has partial support for EJB 3.1.
SCOP is a library for writing distributed applications. The functionality includes message-passing, events, and RPCs. It is primarily aimed at C++ programs on Linux, or Java anywhere. Much simpler than CORBA, it is easy to learn, general-purpose, fairly fast, thoroughly documented, complete, and free.
SwitchRMI is a framework for remote method invocation from Java that allows the client to choose from one of several RMI protocols. Objects can be made available over a number of transports; HTTP and SMTP are implemented. Any object vended can respond to an RMI request in any one of the supported protocols. Clients and servers can interact with third party implementations of supported protocols. New protocols and transports can be plugged in to the framework at runtime.