Computer support for cooperative work requires the construction of applications that support interaction by multiple users. The highly dynamic and flexible nature of cooperative work makes the need for rapid user-interface prototyping a central concern. We have designed and developed a software architecture that provides mechanisms to support rapid multiuser-interface construction and distributed user-interface management. Rapid prototyping requires mechanisms that make the information determining interface configuration visible, accessible, and tailorable. We developed the architecture as part of a project investigating support for the cooperative work of air traffic controllers. Extensive use of prolonged ethnographic investigation helped to uncover the nature of cooperation in air traffic control. The aim of the architecture is to support an environment in which a multidisciplinary team can experiment with a wide range of alternate user-interface designs for air traffic controllers. Thus, we use examples from this domain to illustrate the architecture.