Last years have seen the raise of several contexts such as Ambient Intelligence, Augmented Reality where Artificial Intelligence is combined with other domains such as Ubiquitous Computing, Sensor Network Technologies in order to provide proactive and responsive services to users. However, these systems are most of the times ad hoc, lacking a conceptual foundation. In this paper we provide a broad overview of mirror worlds, as physically situated agent societies, useful in particular as a framework for investigating inter-disciplinary aspects – from cognition to interaction, cooperation, governance – concerning future smart environments and cities shaped as large-scale mixed-reality systems.