Aside from cocaine scoops, I can't think of many instances of folks cultivating their fingernails to use as tools. In Japan's Shiga Prefecture, however, exists a traditional tapestry weaving tradition called tsumekaki hon tsuzure ori that reportedly goes back 4,000 years, and which requires the artisans to file grooves into their nails in order to work the thread:
Here's what they're then able to do with these funky nails:
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I admire their dedication to craft. All I have to do is keep my nails short enough to not hit the keyboard keys.