Game design process creates goals, rules, and challenges to define a game that produces desirable interactions among its participants. Modeling the way in which players interact with the game requires among others the definition of game rules, plot, connection between player and the game, etc. ACTA (ACTivity Analysis) is a general purpose finite state machine (FSM) description language for rapid prototyping of smart games. ACTA facilitates smart game design by intervention professionals who are not familiar with traditional programming languages . Professionals are able to model the game’s logic and interaction using a straightforward and intuitive notation which can be customized for every different game. In order to support a customized scripting vocabulary, a reflection-oriented model was adopted allowing dynamic linking between ACTA generated rules and multiple data types. Windows Workflow Foundation (WF) is the “glue layer” connecting AC TA’s scripting vocabulary with the application internals. Moreover, developers can use ACTA not only for developing event -driven sequential logic games, but also for applications of behavior composed of a finite number of states, transitions between those states and actions , as well as for applications based on rules driven workflows. As a case study illustrating the usefulness and benefits of ACTA, a body posture imitation game, called Mimesis game, was developed based on occupational therapy expertise and practice.