We envision a world of mobile users in an unobtrusive ubiquitous computing environment that couples a computational model, digital media, and virtual representations of the physical world. Hundreds of embedded computers support the information and computational needs of each user. Users, applications, and computing devices move. The location of users and devices drives applications and resource management. Users have anytime/anywhere access to information, the network, and computational resources. Within this world, applications that make effective use of resources to support the activities of users must be simple and efficient to construct. Changes to the physical environment alter the computational model and information space of the users. Similarly, changes to the computational model and information space may alter the physical environment. We call this environment an \emph{Active Space}. We propose a systems software infrastructure that functions in much the same way as a traditional operating system. However, instead of managing resources within a computer, it manages the computational resources within a physical space. In this paper, we describe this systems software architecture and the results of an experimental implementation called GaiaOS.