SiloRider is a command-line utility that lets you implement the POSSE model on a website. This is how it works:

It reads your website’s main page (or whatever URL you supply) and looks for Microformats markup.
It reads a configuration file where you describe which “silos” (i.e. external services) you want to post your content to.
It reads a local cache file to figure out which content has already been posted where, so it only posts new content.
It actually posts that content to each silo.