A gantry crane is a type of crane that is supported by one (semi gantry) or two legs and it straddles it's workload.  Gantry cranes are typically wheeled and may or may not run on rails.  A workstation or portable gantry crane is a very versitle gantry.  The height on many models may be adjustable and since it is usually wheeled it is easy to move around your shop. Workstation/Portable gantries can range from 1 - 5 tons.