Jogger is a project which uses the Jabber protocol as a posting mechanism for weblogs. Very interesting as the Jabber protocol is completely XML and extensible.
The project is still in its infancy and things are just coming up somehow. Apart from supporting RSS, there is also something on the wish list called „Jogger Syndicated XML“:
Jogger Syndicated XML was created in order to provide users with a way to fully integrate with their stored content. Using this format requires you to write the interface to your stored content by parsing the data that you request in this format. You will have the power to write a complete interface to your stored data in this manner