We introduce the Boom Chameleon, a novel input/output device consisting of a flat-panel display mounted on a tracked mechanical boom. The display acts as a physical window into 3D virtual environments, through which a one-to-one mapping between real and virtual space is preserved. The Boom Chameleon is further augmented with a touch-screen and a microphone/speaker combination. We present a 3D annotation application that exploits this unique configuration in order to simultaneously capture viewpoint, voice and gesture information. Design issues are discussed and results of an informal user study on the device and annotation software are presented. The results show that the Boom Chameleon annotation facilities have the potential to be an effective, easy to learn and operate 3D design review system.