Much progress has been made on interactive behavior development tools for expert programmers. However, little effort has been made in investigating how these tools support creative communities who typically struggle with technical development. This is the case, for instance, of media artists and composers working with interactive environments. To address this problem, we introduce ZenStates: a new specification model for creative interactive environments that combines Hierarchical Finite-States Machines, expressions, off-the-shelf components called Tasks, and a global communication system called the Blackboard. Our evaluation is three-folded: (a) implementing our model in a direct manipulation-based software interface; (b) probing ZenStates' expressive power through 90 exploratory scenarios; and (c) performing a user study to investigate the understandability of ZenStates' model. Results support ZenStates viability, its expressivity, and suggest that ZenStates is easier to understand-in terms of decision time and decision accuracy-compared to two popular alternatives.