Virtual reality technologies have been experimented for several years for post-stroke motor rehabilitation, but there is too little diffusion of these systems among medical facilities and none among patients. Our objective is the development of an interactive system to assist motor rehabilitation of the upper limb after a stroke, which retains the medical benefits of traditional post-stroke methods while reducing human costs (usable with minimal supervision) and materials (general public), and facilitating active patient participation. System architecture, 3D interactions and virtual content are based on an iterative, user-centered design methodology with patients and therapists. The system allows users to perform repetitive and intensive tasks with the upper limb. The paretic hand is tracked with a low-cost depth sensor. Kinematic performance is monitored and visual feedbacks are proposed. Preliminary tests were conducted on a non-immersive prototype, with eight patients and a target pointing task. The results showed good usability and high acceptance from the users.