XML-RPC is a remote procedure call system using HTTP requests carrying XML data in distributed systems. There are two free implementations of XML-RPC in Common Lisp.

Chris Double wrote a client library that is now a part of Corman Lisp, but a version adapted by Eric Marsden for CMUCL and CLISP is available from http://emarsden.chez.com/downloads/.

A second implementation for a variety of Common Lisp implementations is S-XML-RPC.

A third implementation tested with SBCL but should work with others supported by its dependencies is rpc4cl.

There is some documentation, pertaining to other-language software and XML-RPC—possibly, would be helpful, for an introduction about XML-RPC—for example: XML-RPC HOWTO.