Abstract: Over the past 8 years there have been numerous attempts to develop add-ons to the X Window System that enable basic sharing of arbitrary X applications. These systems have never been much more than interesting and marginally useful incremental improvements to the capabilities of X. It is our thesis that there are as-yet-unexplored opportunities for the development of new window systems that provide integral, full-featured support for collaborative work and retain substantial backward-compatibility with X. In this paper we present our design for such a window system.