NEPOMUK is described as a Social Semantic Desktop. NEPOMUK stands for Networked Environment for Personalized, Ontology-based Management of Unified Knowledge. The project is developing a comprehensive solution for extending the personal desktop into a collaboration environment which supports both the personal information management and the sharing and exchange across social and organizational relations.
NEPOMUK technology is incorporated into the current KDE releases, see http://nepomuk.kde.org
See the NEPOMUK Blog articles for additional details.