If your first thought is "What's the difference between corsets and waist cinchers?" the main answer is length. Corsets go from your hips to your bust, while waist cinchers only go to beneath the bust (hence the name underbust corset).
Both corsets and waist cinchers can help to reduce and slim your waist, and give you more of an hourglass shape. In certain styles, a waist cincher will enhance the breasts more, since the underbust placement will give them extra lift and oomph. Some styles of "fashion" waist cinchers are shorter and fit mainly around the waist, acting as more of a lingerie accessory.
Like corsets, waist cinchers can make great underwear as outerwear pieces. Pair them with a slim-fitting top and and your favorite jeans or use it somewhat like a belt with a slinky dress.
Waist cinchers are great for women who like open cup lingerie and want to expand past open cup bras and teddies. They're also nice because they're not as commonly used as corsets, so wearing one will get an even bigger reaction! What do you think, divas? Are waist cinchers something you would try?