This paper introduces an easy-to-use decision support system for COllabOrative DEsign named CO2DE. We examine the system particularly for the design concept filtering and selection stages considering the importance of conceptual design although the proposed framework can facilitate a design task, which is recurrent in many design phases. First, the paper briefly reviews what methods can be applicable to each step of the conceptual design process, and then describes the prerequisites for mathematical method-based design concept filtering and selection processes. Secondly, detailed explanation about the process and main modules of the proposed system are provided with a small satellite design case study focusing on (1) what the inputs and outputs of each module are, (2) what information should be specified by design participants, and (3) what results can be obtained from the system. Thirdly, the paper discusses the advantages/limitations of the system and the main difficulties and barriers for the future implementation. Finally, the paper provides a useful guideline to those who want to develop a decision support system for collaborative design by which they can minimise the need for critical refinement and serious modifications of the design at the subsequent design phase.