The spherical torus/tokamak (ST) is a potentially attractive configuration for narrowing scientific and technical gaps to a fusion demonstration power plant and as a more compact and/or modular fusion power source. Due to a reduced plasma surface area to volume ratio, the ST configuration offers the potential to access high power exhaust heat fluxes and high neutron wall loading in devices of modest size. Further, due to increased ability to utilize magnetic pressure to confine a given plasma pressure, the ST may also offer fusion solutions with reduced magnet mass and increased mass power density. Potential fusion development and energy production applications of the ST include: divertor and first-wall heat-flux mitigation research and development (including tests of advanced divertor configurations and liquid metals), neutron sources with low-to-moderate fusion gain (Q=0.1-1) for hybrid applications, neutron sources with moderate gain (Q=1-5) for fusion nuclear science and component testing including breeding blanket development, higher gain (Q=5-10) systems for electricity break-even in a pilot plant, and high gain (Q > 10) modular (Pelec = 100-500MWe) and larger-scale (Pelec = 500-1000MWe) fusion power plants. Details of these applications including major scientific and technology needs and gaps for fusion energy development are described in this paper. Motivations for utilizing the ST for these applications and remaining physics and technological gaps to be addressed to realize the application are also discussed.