"Sherpa Calendar is a Windows / PC Platform (based) intelligent calendar application (iCal compatible) that allows anyone to easily publish and consume RDF based calendars and their HTML representation. Users create semantic content without even knowing it!"
"SherpaFind is a calendar search engine for machine understandable RDF and ICS representations of intelligent calendars and events. SherpaFind allows anyone to quickly and easily search for calendars of interest and preview or subscribe to their iCal or RDF representation. An event search capability will be added very soon. "
Their technology overivew shows they're using Apache, MySQL, PHP and the like: