The last 10 years have seen a massive increase in the amounts of Open Access publications available in journals and institutional repositories. The existence of large volumes of free state-of-the-art knowledge online has the potential to provide huge savings and benefits in many fields. However, in order to fully leverage this knowledge, it is necessary to develop systems that (a) make it easy for users to access, discover and explore this knowledge, (b) that lower the barriers to the development of systems and services building on top of this knowledge and (c) that enable to freely analyse how this knowledge is organised and used. In this paper, we argue why these requirements should be fulfilled and show that current systems do not satisfy them. We also present CORE, a large-scale Open Access aggregation system, outline its functionality and architecture and demonstrate how it addresses the above mentioned needs and how it can be applied to benefit the whole ecosystem including institutional repositories, researchers, general public and government.