Many tools exist for developing real-time distributed groupware, but most of these tools focus primarily on the performance of the resulting system, or on simplifying the development process. There is a need, however, for groupware that is both easy to build and that performs well on real-world networks. To better support this combination, we present a new toolkit called GT/SD. It combines new and existing solutions to address the problems of real-world network performance without sacrificing the simple programming approach needed for rapid prototyping. GT/SD builds on the successes of earlier groupware toolkits and game networking libraries, and implements seven ideas that help solve problems of network delay, quality of service, rapid development, flexibility, and testing. Categories and Subject Descriptors H.5.2. [Information Interfaces]: User Interfaces—prototyping. D.2.2 [Software Engineering]: Design Tools and Techniques— user interfaces. General Terms Performance, Design, H...