Abstract. UML diagrams have become the de-facto standard for the visual modeling of software systems. The creation and discussion of these diagrams is a critical factor impacting the quality of the artifacts under development. Traditionally, facilitating the collaboration of globally distributed team members with heterogeneous system environments has been a costly and time-consuming endeavor. This paper aims to advance the state-of-the-art of model-based development by providing a collaboration environment, which supports the synchronous distributed creation and manipulation of UML diagrams and also lowers the technical entry barriers for participating in the modeling process. We present a prototypical implementation of a collaborative editor for synchronous lightweight modeling (SLIM). Applying innovative techniques, which only rely on functionality natively supported by modern web browsers, technical issues impeding clients to be integrated into the collaborative environment are avoi...