In collaborative virtual environments, users must often perform tasks requiring coordinated action between multiple parties. Some cases are symmetric, in which users work together on equal footing, while others are asymmetric, in which one user may have more experience or capabilities than another (e.g., one may guide another in completing a task). We present a multi-user virtual reality system that supports interactions of both these types. Two collaborating users, whether co-located or remote, simultaneously manipulate the same virtual objects in a physics simulation, in tasks that require low latency networking to perform successfully. We are currently applying this approach to motor rehabilitation, in which a therapist and patient work together.