Co-located multi-user virtual reality systems enable natural collaboration in shared virtual worlds. Users can talk to each other, gesture and point into the virtual scenery as if it were real. These systems either use head-mounted displays or novel stereoscopic multi-viewer projections to provide multiple tracked users with individual 3D images. Virtual Seating Bucks and assembly planning in the automotive industry are good examples, where each of the technologies have their specific advantages. The design of appropriate input devices and interaction techniques for such environments and for three-dimensional environments in general is still a challenging research topic. We will present some of our interface developments including the GlobeFish and the Spheron. Both are six-degree-of-freedom devices, which allow for natural separation of translational and rotational 3D input. Our findings indicate that such a design leads to better performance in common 3D manipulation tasks than the use of integrated six-degree-of-freedom controllers. Furthermore, we show how the adherence to established social protocols for formal group presentations can be facilitated in shared virtual worlds.