This is a little tool which enables you to easily call RPC services with any request you want. You can either write the request in the form of a javascript function call using JSON to encode your data, or you can formulate the XML directly. (You can also see the generated code for the call you want to make, great for learning.)
The code itself is not beautiful - this was a quick job I did when I was working with a lot of RPC services to make my work faster, so it is provided "as is" - however feel free to pull it.
The tool is using Cook's XmlRpc and Newton's Json libraries.