Transparent displays can serve as an important collaborative medium supporting face-to-face interactions over a shared visual work surface. Such displays enhance workspace awareness: when a person is working on one side of a transparent display, the person on the other side can see the other's body, hand gestures, gaze and what he or she is actually manipulating on the shared screen. Even so, we argue that designing such transparent displays must go beyond current offerings if it is to support

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... ollaboration. First, both sides of the display must accept interactive input, preferably by at least touch and / or pen, as that affords the ability for either person to directly interact with the workspace items. Second, and more controversially, both sides of the display must be able to present different content, albeit selectively. Third (and related to the second point), because screen contents and lighting can partially obscure what can be seen through the surface, the display should visually enhance the actions of the person on the other side to better support workspace awareness. We describe a prototype system we built to satisfy these requirements called FACINGBOARD-2, where we concentrate on how its design supports these three collaborative requirements.