The roofing nailer (Image 1) drives nails through shingles and other roofing materials and holds the nails in a coil (Image 2). Its trigger remains depressed during operation: the firing action is triggered by depressing the foot.
The Plasti-Tacker from Hitachi (Image 1) shoots nails and plastic washers simultaneously. It's used for attaching house wrap, roofing felt and insulation siding. It drives a small nail followed by a plastic cap that ensures that the nail holds the material in place without completely penetrating it (Image 2).