An Underhung Crane is a type of overhead crane with end trucks that ride on the bottom flange of the runway beams instead of on top. Sometimes these overhead cranes are called "under-running" instead of underhung.
These runway beams are often suspended from the roof, which eliminates the need for extra support columns. This can be advantageous if floor space and the need to reduce obstructions is a major issue in your facility.
An underhung crane may even be appropriate with sloped ceilings or multiple crane systems. These cranes can be manual or motorized and can feature radio controls.