There are abundant sources of metal-oxide-based wastes from industries such as electronics and metal production, which generally have a detrimental effect on the environment when not recycled. In this concise review, we aim to provide a brief overview of the state-of-the-art research on how these metal-oxide wastes are being used by the scientific community in the applications of energy storage, catalysis, and sensing. We focus on three important waste streams: E-waste, waste from the production of metals, such as red mud and slag, and waste from metal recovery, for example, rusted wires and discarded capacitors. We review some promising routes for obtaining high-quality metal-oxide nanoparticles and nanowires and critically review potential pitfalls that hinder the wide-scale application of these waste-streams.