This is the best one:
Question: Is there a metric version? My mom lives in Europe and I don’t want to send her one that won’t work in her country.
Answer: Yes, the US version has the slicers spaced at 0.375". The metric version has the slicers spaced at 9.525 mm. I hope that helps.
Egg separator?
In my house we use long-handled teaspoons for all teaspoon purposes, but we have two “normal” ones that are only taken out of the drawer when the breakfast is soft-boiled eggs.
Corkscrews are not useful for anything other than pulling corks.
I just watched my wife using one to retrieve boiled eggs from the pan. A job which the utensil did more admirably than any spoon.
I’ve used mine to roll thin dough for savoury crackers.
RIP Autolycus
My Swiss SO’s family (and apparently every family in Switzerland, or at least every family worth knowing) has one of these devices, whose sole purpose is to shave a particular kind of cheese into thin spirals. Whether it gets used for anything else I do not know, but I find it hard to think of anything else that I know of that has such a specific intended use.
I use my pasta maker for rolling out fondant.
A pizza cutter is also great for cutting fondant strips for decoration.
I use my grater to make spaetzle, so that’s three things spaetzle turns into a muti-tasker.
Williams-Sonoma has an abundance of products that really only have one use
cherry pitter? strawberry huller? mango pitter? egg poacher? yeesh
A. I WANT ONE!
B. Crap. They don’t ship to the US. 
If you scroll down on that page, there are offered for sale various other food products designed to be shaved on that very device, such as nougat and chocolate.
It might be abused for shaving other things, but the *intended *purpose of the device is to shave nothing but that cheese, as the manufacturer themselves note:
There must be somewhere in the US that has them for sale…
Yep, there is - surprisingly expensive, though. :eek:
Roomie has this Julienne peeler tool.
We have two things I can think off offhand that have just one specific use each; a bottle opener (and it is just that) and a garlic press.
Actually I use mine for lots of other things. The two major ones are dishing out green beans (the longer ones, not the cut up frozen ones), and scooping bones and other solids out of a stockpot :).
The garlic press is used to crush allspice and peppercorns for some recipes.
The basic can opener (the kind with a pointy thing at one end for puncturing cans and a rounded tip at the other for bottles) actually rarely gets used for that purpose. How many cans have just liquid in them? For us, just tomato sauce - and when we’re using that we’re usually also using whole tomatoes which require the regular can opener. However, we frequently use the pointy end for puncturing plastic seals on things and/or opening packages: one point, can’t go too deep into the contents, perfect for drawing a slit down the sealing tape.