This grater/zester was the first new tool I’d found in a long time that seemed to really change my cooking habits. It’s now on my list of required tools.
I use it for citrus zest and for grating nutmeg, ginger, chocolate, and fresh horseradish (which you can buy at farmers’ markets here in San Francisco. You can plant it, too, but that’s another story.) as well as for hard cheeses such as Parmesan. It makes a lovely, light dusting of the cheese.