Think of a coffee percolator as a combination between a tea kettle and a coffeemaker. The percolator has a thin tube which runs up the center and leads into a chamber where coffee grounds are placed. As water is heated in the bottom of the percolator, it is forced up the tube and into the grounds before running back down into the water chamber. This process repeats continuously until the coffee is ready to drink.
There is a reason why percolators come with a regulated warmer and not a flat bottom for the stove top: a tea kettle can boil water until it whistles without affected the tea's flavor. But boiling coffee will cause it to have a bitter taste. Thus, percolators are temperature regulated to prevent foul-tasting coffee. This temperature regulation system turns out perfect coffee (when supervised) every time.
Most percolators still need attention so you don't overheat the coffee. Essentially, the longer you let the percolator run, the stronger the brew. This unique system is favored by some coffee purists for its flexibility. Percolators through Everything Kitchens are available from brands like Regalware and Cuisinart, ranging in size from 12 cups up to 110 cups.