The falling cost of display technology has led to a proliferation of large public displays. However, to move beyond simple advertising kiosks and use public displays as a community tool typically requires a lengthy ethnographic approach. In this paper we describe CATS, a rapid UI design methodology that we developed and used to create a public display system for stimulating community interaction during a large university alumni event. The CATS methodology relies on the co-evolutionary process between (C)oncept design, (A)ctivity design, and (T)echnology design through (S)cenario dramatization. Each of the three design strands occurs simultaneously and is connected through a central scenario dramatization process, in which study participants selectively enact various aspects of the interaction in order to verify and explore different design issues. In this article, we briefly describe the CATS methodology and report on our use experiences. © 2011 ACM.