Complex design problems require members of project teams go beyond individualistic work to engage in joint activity of generating new insights, new ideas, and new artifacts. Excellence in the design of GUIs requires creative problem solving. It is widely accepted that creative problem solving is most effective when individuals or groups employ a cyclic process of divergence-convergence consisting of three phases. In this paper we propose a collaborative environment for GUI design and evaluation, at the core of which is a process-based Agent Facilitator (AF). The advantage of this AF lies in its 1) focus on process of managing group dynamics rather than the content of the discussion, 2) democratic and non-obtrusive facilitation style, 3) strong feedback mechanism and 4) transparent collaboration and consensus making process. We discuss the system architecture and the implementation of a prototype extending the online chat mechanism. Although our initial effort has focused on the domain of Graphic User Interface (GUI) design, this framework is applicable to other design domains.