A gantry crane is a freestanding steel A-frame on its own legs and casters, it does the job of a jib or bridge crane without tying into a wall, column, or ceiling. Roll it to the lift, pick the load, roll it to the next one. That makes it the fastest way to add overhead lifting to a bay, dock, or work cell that was never built with a fixed crane in mind.
Frames come adjustable-height (knockdown, so the whole unit breaks down for storage or a move between sites) or fixed at one height and span for a dedicated lift point. Pair either with an electric or manual hoist, a trolley for positioning under the beam, and the rigging hardware, beam clamps, controls, to finish the pick. Because capacity is rated on the frame, hoist, and trolley together and freight on steel gantries runs heavy, this is a quote category: send your lift weight, height, and reach, and we spec the whole rig as one system.