A manual contraption for slicing lemons and limes into perfect wedges that isn't my two hands may not be a groundbreaking addition to the world, but as a bar tool I'd pretty sure I'd use it at least as much as my shaker, and probably only slightly less than my boobs ice luge mold.
I personally don't enjoy cutting lemons and limes because I gnaw the crap out of my cuticles and their juice's infiltration into my open wounds stings like Ali's fist coated in sulfuric acid. I also think Norpro's slicer merits inclusion at BBQs and cocktail parties that begin as organized and refined events with plenty of pre-cut lemon and lime wedges, but devolve after a few hours into drunken shit shows, with hosts just throwing out whole fruits and knives for guests to have at it themselves. Then you get all this hacked-up, oddly-shaped, cootie-covered citrus strewn about cutting boards and countertops because wasted people can't do anything right, especially demonstrate fine motor skills.
The Norpro slicer easily guillotines lemons and limes into 8 perfect wedges. It measures 3-1/2" high, and is compact enough for drawer or cabinet storage.