We present two systems for simulating and designing agents, respectively. The first, the Abstract Force Simulator (AFS), is a domain-general simulator of agents applying forces; many domains can be characterized in this way. The second, Hierarchical Agent Control (HAC), is a general toolkit for designing an action hierarchy. It supports action abstraction, a multilevel computational architecture, sensor integration, and planning. It is particularly well suited to controlling large numbers of agents in dynamic environments. Together, AFS and HAC provide a very general framework for designing and testing agents.