MindRaider: Outliner and More

freshmeat.net: Project details for MindRaider
MindRaider is a Semantic Web outliner/mind mapper. It aims to connect the tradition of outline editors with emerging technologies. MindRaider’s mission is to organize not only the content of your hard drive but also your cognitive base and social relationships in a way that enables quick navigation, concise representation, and inferencing.

Among other things it has support for OPML.