An apple corer is a hand-operated tool designed to facilitate removing the cores from apples. The utility of a corer becomes evident when you are processing large quantities of apples for canning, drying, etc.
An apple slicer is a device designed to both core and slice apples. There are simple hand ones that work by dint of brute force, and machines that work through hand cranking.
Bean slicers are tools designed to French-slice green and runner beans. They allow fast, efficient transformation of beans into thin, uniformly-cut pieces.
A butter pat slicer is a tool designed to cut a stick of butter into even pats of butter. You can also use one to slice bananas, or to mark up rolls of cookie dough for cutting.
Cucumber slicers allow a cook to create very thin, uniform slices of cucumber. The name is a bit of a misnomer, as the devices can also be used for other produce as well.
A doughnut cutter is a special hand-held and operated cutting tool for making doughnuts. In rolled out dough, it cuts out a circle, and then a small circle at the centre of that circle.
An egg slicer is a two-part device for slicing a peeled, boiled egg into thin, uniform slices of egg.
A girolle is a special tool to help you turn your Tête de Moine cheese shavings into roses.
A mandoline is a food slicer. Instead of moving a blade over the food, as you do with a knife, you move the food over a blade. It is a manual device, with no electricity required.
A melon baller is a tool designed to scoop melon flesh out in small, perfectly shaped balls, which you then serve in bowls or incorporate into a fruit salad.
An olive pitter is a tool to remove the pit (aka stone) from an olive. Using one is the only way to pit olives at home without chopping or mangling them.
A pineapple slicer slices and peels a pineapple at the same time. It works like a big corkscrew that works its way downwards into the pineapple to remove the fruit, while leaving the rough skin behind.
A V-slicer, like a mandoline, is a mounted slicing tool. But instead of its sharp metal blade being a straight, diagonal line, it is V-shaped. There are different brands, but almost all are less expensive than mandolines.