XML-RPC is a format for remote calls using XML messages. Sounds complex, but implementing an XML-RPC interface into an application allows other services to communicate with it.

Currently, there are three APIs supported: the Blogger API, the metaWeblog API, and the Movable Type API. If you want an examples of a client that uses these interfaces, try w.Bloggar (Windows) or Ecto (MacOS).

The available calls to the interface are described in the development documentation, which can be viewed online.