Requirements are the heart of Information Systems development because they determine how the system will operate. There- fore, requirements elicitation is a critical activity of the information systems development life cycle. Recognizing the im- portance of collaborative work and the huge difficulty of gathering stakeholders at the same time and place, researches have been proposing web collaborative tools to elicit requirements. In this article we present a game-based collaborative tool called iThink that aims at improving the participation in a requirement elicitation process. iThink takes advantage of the associa- tion between “gamification” concepts and the six hats of thinking method for collecting both new requirements and feedback about existing ones and for presenting the requirement elicitation process in a form of a collaborative game. Two case-studies, involving several stakeholders, are also presented with the purpose of evaluating the effectiveness and acceptance of this tool