The Irish Mail is an arm powered device that you can build yourself. Like a bicycle, it uses only your own power to move you around, but is much more powerful than walking on your own two feet. Unlike a bicycle, operating an Irish Mail builds your arm muscles, especially your biceps and triceps.
Most ordering kits tend to be child-sized. Adults will want to build theirs larger, and perhaps attach a cart to the back for storing items. Both would benefit from the addition of rear-view mirrors, reflectors, and other such safety features.
Adults who replace one short drive with a car with a short trip with the irish mail can expect to lose up to 20 pounds per year. Take that, obesity.