The food mill is an entirely manual utensil that is simple, highly efficient and inexpensive.
How does it work?
It's a flared metal or plastic container, with a grid of more or less fine holes lining the bottom.
A plate, which turns with a simple crank, forces the poured preparation through the grid.
Place the mill on a container (saucepan, salad bowl, etc.) - it has 3 feet for this purpose - pour the preparation into it and turn the crank, "grinding" until all the preparation has passed through the grid, turning the crank in the other direction from time to time to clear the grid.
At the end, all that's left to do is to discard (in the composter if possible) the hard parts remaining on the grid, and start again.
It's super-simple and highly effective.
Vegetables only?
It's called a vegetable mill, because that's its original use, but it can be used with any fairly tender, often cooked, preparation that needs to be turned into a kind of purée (some even call it a "potato masher") or coulis, vegetables and soups of course, but also fruit, fruit purée or any other food tender enough for that.
It's ideal for this job, because it works without forcing or pulverizing like a blender would. As a result, mashed potatoes made in a blender quickly become sticky, which is never the case with a food mill.
And above all, of course, it separates.
Making fruit jelly, blackcurrant jelly for example, becomes much easier if you put the fruit through the food mill before cooking it.
An old-fashioned utensil
My grandmother and mother had one, as did I, and I've converted my sons to them.
Over time, though, the principle hasn't changed one iota, the material is a little different: tin-plated iron in the olden days, stainless steel or plastic nowadays, but there's still no need to connect it to a power source, apart from elbow grease of course.
To sum up: the food mill is the essential manual tool for pureeing and separating the hard parts of cooked or fairly soft foods.