A major paradigm of modeling the decision making of autonomous agents is through behavior-based network models. The network consists of distributed behaviors that compete (or cooperate) according to certain relations for governing the agent's behavior in a dynamic environment. This paper presents an effort to develop BehaviorSim that is an educational tool oriented to beginners and/or non-computer scientists to allow them to learn and play with the behavior-based paradigm without involving complex programming skills. The system design of BehaviorSim is presented, followed by a description of its major functions. An illustrative example of a crayfish agent is provided to demonstrate the functionality of this environment. Categories and Subject Descriptors I.6.3 [Simulation and Modeling]: Simulation applications General Terms Simulation of control systems, Behavior-based paradigm, autonomous agents Keywords Behavior-based control, action selection dynamics, mutual inhibition behavi...