Shared window systems allow collaboration transparent, single-user applications interacted with on multiple users' workstations, enabling the members of a cooperative ensemble to simultaneously share and revise information. The paper presents a system capable of sharing applications running under the X Window System. In contrast to previously implemented systems, the present shared window system addresses issues that are crucial for general-purpose use. The shared window system is policy-free, i.e., there are no preferred policies for handling issues such as admission and floor control. Instead, it offers a set of essential mechanisms on top of which various policies and user paradigms may be realized. Further, the system distributes the sharing functionality among all sites involved in a cooperative activity. Measurements have shown a positive impact of this on the overall performance of the system and thus justified the viability of the design decisions taken.>