The CoSy Architecture Schema Toolkit (CAST) is a new software toolkit, and related processing paradigm, which supports the construction and exploration of information-processing architectures for intelligent systems such as robots. CAST eschews the standard point-to-point connectivity of traditional message-based software toolkits for robots, instead supporting the parallel refinement of representations on shared working memories. In this article we focus on the engineering-related aspects of CAST, including the challenges that had to be overcome in its creation, and how it allow us to design and build novel intelligent systems in flexible ways. We support our arguments with example drawn from recent engineering efforts dedicated to building two intelligent systems with similar architectures: the PlayMate system for tabletop manipulation and the Explorer system for human-augmented mapping. Key words: intelligent robotics, artificial intelligence, information-processing architectures, ...