Optically-active solid-state spin systems can offer remarkable single photon emission properties (brightness and indistinguishability), which makes them useful for developing photonic quantum simulators and building blocks of quantum networks. In this talk, I will present the efforts of studying the fundamental physics of optically-active spin systems and integrating these systems in photonic platforms for quantum technologies. First, I will describe all-optical implementations of NMR-inspired protocols for controlling the quantum state of optically-active spins and for the diffraction-limited probing of their nuclear environment. Then, I will discuss the process of coupling optically-active spins to photonic cavities, which provides spin-dependent optical switching capabilities. Finally, I will focus on the applications of spins in photonic platforms for simulating quantum dynamics under complex Hamiltonians, as well as toward the demonstration of photonic repeaters for the efficient distribution of quantum information.