Intriguing browser-based RSS aggregator, NewsMonster [via Ben Hammersley], making full use of its centralised nature: "NewsMonster is backed by a Semantic Web enabled RDF database which allows us to preserve the semantic relationship within documents. This allows NewsMonster to act as an agent on your behalf and help you barter goods and services online. Want to sell your used guitar? No problem. Just create a new advertisement and publish it on your blog". (Hang on, I recognise that used guitar example.) A reputation system and shared ratings are also included.