SMOB: Semantic Microblogging (a distributed / decentralised microblogging system built on RDF and Semantic Web technologies, mainly SIOC and FOAF.)

The SMOB client enables you to publish your microblog postings,the SMOB server,lets you set up your own microblog aggregators,both prototypes are less than 100 lines of PHP code each.
http://smob.sioc-project.org/