Light sources capable of producing very large numbers of entangled photons are key devices for the future development of quantum networks and optical quantum computers. They are the backbone of high rate quantum networks and the key ingredient for the development of a large scale universal quantum computer. Such sources do not presently exist since most existing approaches to entangle photons are probabilistic and suffer from poor efficiency, with the result that they cannot be scaled to large photon numbers. However, there is a solution connected to three recent breakthroughs in the quantum optics community: the possibility to control single quantum dot spins with high fidelity (i), the possibility to generate single photons from semiconductor quantum dots with unprecedented performance metrics using optical micro-cavities (ii), and new theoretical proposals to entangle many photons with a single quantum dot spin (iii). In QLUSTER, top-level experts in these three – currently largely independent - research areas join for the first time to tackle the long-standing challenge of producing many-photon entanglement in a deterministic and scalable way. This is a highly ambitious project, and to keep the risk under control, we explore the most promising spin and cavity platforms as well as progressively implement protocols of increased complexity. The methods that will be applied will facilitate the generation of entangled-photon sources that are exponentially more performant than existing ones, and will provide a resource that has real potential to revolutionize photonic quantum technologies, and therefore the emerging quantum network and computing markets.