The Distributed Simulation Internet (DSI) provides users access to large-scale, complex, active, unpredictable virtual environments. If users are to effectively use these environments, they will require support for understanding and acting in these environments. Support is necessary because humans have a time and space limited span of attention. The Satellite Modeler, Omniview true 3D, and Synthetic BattleBridge projects were undertaken to develop and investigate the interfaces and autonomous agents required to effectively support users of the Distributed Simulation Internet. The Satellite Modeler emulates the near-Earth space environment and portrays models of satellites moving in their correct orbits around the Earth. The motion of the satellites is broadcast to users of the DSI. The Satellite Modeler is intended to function as a training and operational aid for orbital analysts and to help them understand key spatial relationships for satellites in near-Earth orbit. The Omniview project was undertaken to provide interactive control and manipulation of a true 3D image and to thereby assist the user in understanding the activity within the DSI-hosted virtual environment. That project developed an interface that provides the Omniview user with the ease of use that a window, icon, mouse, and pointer GUI interface provides to users of 2D displays. The Synthetic BattleBridge is a system that, like the Omniview, portrays a DSI-hosted virtual environment but does not act in it. The Synthetic BattleBridge is designed to support users in making accurate and timely decisions by providing several different types of cognitive support for understanding and analyzing the activity in a battlespace. In this paper, we briefly describe each project and present some observations and conclusions we have drawn based on our experience with them.