Automation was a milestone in manufacturing during the Third Industrial Revolution, where industrial robots meant the end of a wide variety of routine and monotonous tasks. However, little human-machine interaction was possible. In fact, robots where enclosed within security areas where they could operate preventing any potential human injury and according to a repetitive pattern. With the advent of Industry 4.0, state-of-the-art active security systems are enabling growing worker-robot collaboration, by which human flexibility and machine accuracy merge. Collaborative robots (CoBots) comprise this sort of technology. Boosted by the Internet of Things, Cloud Computing and Big Data, robots in modern manufacturing rely on improved customization, adaptability and quality. In order to explore the potential of this technology, this paper is structured as follows. First, a description of the technology behind modern manufacturing robots. Second, a historical background together with a strengths-weaknesses discussion. Third, a state of the art of current applications in industry and a list of alternatives in the market. Finally, a series of trends concerning the future of the manufacturing industry and existing enterprises that are supporting the change.