Halide perovskites have swiftly been elevated to a subject worthy of serious and extensive research. They are unequivocally an unprecedented class of semiconductors with a broad range of optoelectronic applications. These materials display outstanding properties, which are the results of their direct and tunable band-gap, high electron/hole mobility, strong light-absorption coefficient, and high defect tolerance coupled with low non-radiative recombination rates. Their preparation is also extremely easy and compatible with room-temperature deposition processes. Nonetheless, the toxic nature of lead (Pb and its ions) and the poor stability against moisture, limit their mass production and commercialization. This article thoroughly reviews the recent investigations undertaken to solve these thorny problems by focusing mainly on the structural development and the photoluminescence tuning ability of lead-free perovskite nanocrystals (NCs). In the light of the principles related to crystal chemistry, we present the development of perovskite NCs from mineral prototypes, which leads to a variety of multi component Pb²⁺-free perovskite type compounds. Then, assuming that the ultimate goal is the production of a single-component white-light emission device, we shed light on the development of broadly tunable Pb²⁺-free perovskite NCs with intrinsic emission as well as extrinsic emission achieved by doping with various ions, and on the corresponding energy transfer (ET) mechanism, which governs the color and the photoluminescence emission tuning ability. The present review aims to assist the research which deals with the discovery of new highly stable, nontoxic perovskite NCs, following a strategy associated with excitonic luminescence enhancement, in conjunction with a comprehensive understanding of the role of energy transfer phenomenon, whereby efficient tuning ability is achieved by various dopants.