Directory at www.xmlrpc.com
XMLRPC-EPI A standalone C API for XML-RPC http://xmlrpc-epi.sourceforge.net/
xmlrpc-epi-php is a PHP C extension that utilizes xmlrpc-epi to provide a high performance, easy to use, php native interface to xmlrpc.
This extension is used for PHP.
Incutio XML-RPC http://scripts.incutio.com/xmlrpc/
The Incutio XML-RPC library (IXR) is designed primarily for ease of use. It incorporates both client and server classes, and is designed to hide as much of the workings of XML-RPC from the user as possible. A key feature of the library is automatic type conversion from PHP types to XML-RPC types and vice versa. This should enable developers to write web services with very little knowledge of the underlying XML-RPC standard.
Don't however be fooled by it's simple surface. The library includes a wide variety of additional XML-RPC specifications and has all of the features required for serious web service implementations. phprpc http://sourceforge.net/projects/phprpc/
Keith Devens xml-rpc http://keithdevens.com/software/xmlrpc
Here's a fully compliant XML-RPC client and server written in pure PHP. Only requirements are PHP, and the XML parser you're guaranteed to have if you're using PHP built into Apache (which most people are).
The main benefit of using this XML-RPC library over others is that it uses native PHP datatypes wherever possible and doesn't force you into OO. I'd tried other XML-RPC libraries, and they make you use objects in complex ways just to build your XML-RPC message. With this library, you can build your message using nothing but native PHP datatypes. Since PHP is a high level scripting language, it has most of the type information available to you that you need to build an XML-RPC message. That's called “reflection” :) The library is also fairly small (<500 lines).