Ripcord
Ripcord is an attempt to create an RPC client and server around PHP's xmlrpc library that is as easy to use as possible. You can create XML-RPC, (simplified) SOAP 1.1, and simple RPC clients with one call and then call RPC methods as if they were local methods of the client. You can create a server with one call, passing it any number of objects whose methods it will publish and automatically document.