Traditional graphical user interfaces (GUIs) are mainly designed for an environment consisting of a single display and a set of single input devices. However, in the near future we will be using a number of computers (and other electronic devices). Just as we often combine several physical devices to perform a task in a real world, it should also be possible to use multiple computers more effectively. This paper proposes the notion of multiple-computer user interfaces in a future cooperative environment. We also describe an interaction technique that allows a user to transfer digital information to other electronic devices placed in a physical environment, and a digital whiteboard system that effectively uses a multiple-device architecture.