The World Wide Virtual Machine
Disclaimer: This entry is in no way meant to slight the many other fine distributed frameworks out there. Its just that this one is designed for us non-rocket scientists. :-)
I host a free project here on java.net called the cajo project. It allows any Virtual Machine to easily expose access to any of its selected objects to Remote Virtual Machines, as well as to send any of its selected objects to RVMs. It offers a very simple yet highly flexible framework for applications to work together. Most importantly, any existing object can be made remotely usable, with no changes to its source; an application simply adds this framework, not restructures around its requirements. I have found this unique amongst distributed frameworks.
A client can obtain a remote reference to an exposed object in one of two ways. It can request one explicitly, using just the name of the server, and the name under which the exposed object is registered, if it knows these things. In the framework, this is called static binding. It can also listen for object reference broadcasts, sent from RVMs. This is called dynamic binding. The references can then be freely shared in turn with other remote objects. Exposing an object for remote reference is done conversely; it can be bound locally under a name, or be broadcast to all listening VMs, even both.
Clients can invoke the remote objects methods, and receive the resulting return, just as though it was a local object. How does the client know how to use a remote object? The object can implement a getDescription() method, it would provide detailed usage information. The object often implements a getProxy() method, it would generally return a graphical user interface component with which to interact with the remote object. The framework also features a standard generic client, which can be run as applet in a browser, or as an application via JNLP, to remotely host the GUI component.
Any VM can send an object (or remote object reference) to an RVM, as an argument to one of its methods, or by returning it as a method result. The objects will physically exist locally in the RVM, i.e. in the same address space, as its own objects. These objects are known as proxies in the context of this project, as they exist to act in a remote location, on behalf of their sender. The previously mentioned the getProxy() method is used to return a GUI proxy object.
The framework borrows from the best concepts of Jini, CORBA, and DCOM, but it is far smaller, as powerful, and much simpler to use. The core framework consists of only two packages; a total of only 13 small class files. It can be so small and easy to use, as it does not impose any application semantics beyond those outlined above. It comes with a detailed example file, ample documentation, and several support fora. It is completely free, licensed under the GNU LGPL, to allow both free and proprietary applications to operate together.
The framework is currently running on all Java Runtime Environments; J2EE, J2SE, and even J2ME. It is in active use on Linux, Windows, Solaris, and OSX systems. The goal of the project is to foster the creation of a WWVM. This is an exciting shared space of applications and object libraries, where they all appear and are used as though they were local, to foster the creation of new dynamic, interactive application networks. All VMs are free to join, from big mainframes, to tiny PDAs. (You can use any JVM compatible language, even Java)
Please come visit the WWVM community, all are welcome. Participants needed. :-)