Equal is a brand name for Aspartame which is an artificial sweetener that is about 200 times sweeter than sugar. According to the manufacturer, "Aspartame is made by joining together two amino acids with a methyl ester group. All of these components are also found in foods eaten everyday." Although FDA approved there has always been a lot of controversy about how healthful Aspartame is.
The product is available in several forms including a version called Spoonful which can be used for cooking and is used cup for cup the same as you would sugar.