One of the main shortcomings of most Virtual Reality display systems, be it head-mounted displays or projection based systems like CAVEs, is that they can only provide the correct perspective to a single user. This is a significant limitation that reduces the applicability of Virtual Reality approaches for most kinds of group collaborative work, which is becoming more and more important in many disciplines. Different approaches have been tried to present multiple images to different users at the same time, like optical barriers, optical filtering, optical routing, time multiplex, volumetric displays and lightfield displays among others. This paper describes, discusses and compares different approaches that have been developed and develop an evaluation approach to identify the most promising one for different usage scenarios.