From Seo Wiki - Search Engine Optimization and Programming Languages
The API is implemented as an XML-RPC web service with three methods whose names describe their function: metaweblog.newPost(), metaweblog.getPost() and metaweblog.editPost(). These methods take arguments that specify the blog author's username and password along with information related to an individual weblog entry.
The impetus for the creation of the API in 2002 was perceived limitations of the Blogger API, which serves the same purpose. Another weblog publishing API, the Atom Publishing Protocol became an IETF Internet standard (RFC 5023) in October 2007.