Avatars' mobility is an essential element to design, validate, and compare different distributed virtual environment architectures. It has a direct impact on the management of such systems because it defines the workload associated with the areas in the virtual world. Currently, a relevant part of this evaluation is conducted by means of synthetic traces generated through mobility models. Despite that, in the last decade, several models have been proposed in literature to describe avatars mobility. However, a standard methodology that drives researchers in their evaluation does not yet exist. In order to alleviate this issue, we present TRACE, an open source tool supporting the generation and analysis of traces by means of embedded mobility models. TRACE's ultimate aim is to facilitate the evaluation and comparison of virtual environments and allow researchers to focus on developing their solution rather than spend time to code and test custom mobility traces. TRACE provides a unified format to describe the traces. It enables scalable and efficient trace generation and analysis for thousands of avatars with seven built-in models.Also, it defines APIs enabling the integration of additional models, different configurations of the environment, and several built-in metrics to analyze the generated traces. KEYWORDS distributed virtual environment, mobility model, multiplayer games, open source 1 INTRODUCTION On-line gaming entertainment has received lots of popularity in the last decade from both industry and research communities. This attention is justified by the economic growth of the sector, in which massively multiplayer online games such as World of Warcraft 1 or Second Life 2 represent a remarkable member. From a practical point of view, massively multiplayer online games that are large-scale distributed applications are a synchronous, persistent, and interactive virtual environment that allows a huge amount of users worldwide to share a real-time virtual environment.In these applications, each individual is in control of a virtual character called avatar. The avatar is free to move in a virtual world, perform actions, activities relative to the game, and meet other avatars.One of the largest area of research in this context is to foster the transition of virtual environments from client-server to distributed applications.Such approaches, broadly referred to as distributed virtual environments (DVEs), 3 aim at achieving scalability and cost-effectiveness, by orchestrating the support of the virtual environment to exploit the computational and network resources of the users of the DVE. Common approaches for the definition of the distributed support are based on unstructured 4,5 and structured 6,7 peer-to-peer technologies, as well as more centralized technologies like cloud computing 8 .In such distributed approaches, a user resource (ie, peer) concurrently works both as client for an (usually single) avatar and as server for a part of the virtual world. This organization allows to exploit the inherent scalabili...