In the world of warehousing, distribution and general material handling a stacker is a machine that combines features of a walkie or walk-behind pallet jack with features of a lift truck where an operator would typically sit or stand while driving like a counterbalanced, reach or straddle lift truck. These combination forklifts are typically referred to as walkie stackers.
The tractor or drive unit of a powered stacker will be the same or very similar to a walk-behind pallet jack or pallet truck. Light-duty stackers may not use a powered drive unit. Some stackers are available with a reach mechanism or pantograph that allows the forks reach out to pick up or put away palletized loads in warehouse racking. Other stackers will have masts similar to counterbalanced lift trucks