PHP XML-RPC client/server library

 XML_RPC2 is a pear package providing XML_RPC client and server
 services. XML-RPC is a simple remote procedure call protocol built
 using HTTP as transport and XML as encoding. As a client library,
 XML_RPC2 is capable of creating a proxy class which exposes the
 methods exported by the server. As a server library, XML_RPC2
 is capable of exposing methods from a class or object instance,
 seamlessly exporting local methods as remotely callable procedures.