Carbon-based nanomaterials, in their many forms, have been one of the main foundations of research and development in material science and related subjects. Carbon is crucial for many technical uses, from pharmaceuticals to catalysts, and it can take many different forms, including nanoparticles (NPs), polymers, and supramolecular complexes. The most important allotropic modifications of the nanocarbon include fullerene, carbon nanotubes (CNTs), graphene, carbon nanofibres, and carbon dots (CDs). CNTs have numerous applications in nano-electromechanical systems. CNF structures are frequently preferred as energy storage and sensing electrode materials due to the rapid current transmission and larger surface area. By virtue of their distinct optical, electrical, and catalytic capabilities, carbon dots are of interest in the development of biosensors and energy applications. Herein, the role of the unique behaviour of key carbon allotropes like CNT, CNF, and CNP in the development of energy and sensing applications is explained with research reports.