“XML-RPC Client is a free Cocoa-based developer tool for Mac OS X Tiger that allows you to access and debug XML-RPC web services from the comfort of your desktop.”
#xml-rpc
Transfer
Cross-posting (WP –> WP) plugin that allows you to use one installation as the main one, and cross post to other installs via XMLRPC.
LJ Client API
The official documentation for the LiveJournal API.
json-xml-rpc – Google Code
The client libraries available here allow requests to be made in either XML-RPC or JSON-RPC to the same service, and the server implementations available provide responses according to the type of RPC request provided.