Reusing single-user applications to create multi-user internet applications. Although there are many groupware platforms existing nowadays, collaborative multi-user applications are not yet widely accepted by end-users. In contrast to single-user applications, groupware applications often still have prototypical character and are lacking software quality. In this paper we introduce a three-step approach for reusing existing single-user applications for collaboration-aware multi-user applications. The three-step approach is based upon on our toolkit {it DreamTeam} and its extension {it DreamObjects} . By offering services for communication and coordination as well as data management and user interface development they significantly simplify the transformation of single-user applications into collaboration-aware applications. At the end of the paper we validate our approach with two examples: a diagram tool and a publicly available spreadsheet tool.