This paper presents the design of a wearable robotic forearm for close-range human-robot collaboration. The robot’s function is to serve as a lightweight supernumerary third arm for shared workspace activities. We present a functional prototype resulting from an iterative design process including several user studies. An analysis of the robot’s kinematics shows an increase in reachable workspace by 246% compared to the natural human reach. The robot’s degrees of freedom and range of motion support a variety of usage scenarios with the robot as a collaborative tool, including self-handovers, fetching objects while the human’s hands are occupied, assisting human-human collaboration, and stabilizing an object. We analyze the bio-mechanical loads for these scenarios and find that the design is able to operate within human ergonomic wear limits. We then report on a pilot human-robot interaction study that indicates robot autonomy is more task-time efficient and preferred by users when compared to direct voice-control. These results suggest that the design presented here is a promising configuration for a lightweight wearable robotic augmentation device, and can serve as a basis for further research into human-wearable collaboration.