Acesulfame Potassium is an artificial calorie-free sweetener that is 100-200 times sweeter than table sugar. It is used extensively in commercial baked goods, diet sodas, and other low sugar or calorie products. It is marketed under the brand name Ace-K.
There is some controversy regarding the safety of acesulfame potassium in food.
International Food Information Council's site on Acesulfame Potassium The IFIC is a public relations organization for the sweetener industry.