Media are explored to envision, to design, and to implement platforms for knowledge management within communities. They actively shape, support and develop the community being resident on a medium. We study Intranets as media for knowledge management and provide an agent-oriented model for Intranets. We argue that organization and logical space of a community have to be reconstructed on the medium and that new knowledge and organizational structures can evolve by using the medium. We distinguish as counterparts the organizational structure and the knowledge being represented on the platform and the organizational structure and the knowledge of the community resident on the medium. We propose a media dialog and a media spiral between those counterparts as processes of shaping a community by a medium and of developing and implementing new knowledge and new organizational structures within a community on a medium.