Cream of Tartar is a potassium acid salt of tartaric, produces a creamier texture in frosting, candy, and gelatin desserts.
It helps make egg whites whiter and stabilize them, which adds more volume to meringues (usually 1/8 teaspoon per egg white).
Cream of tartar is especially great to stiffing cookie frosting, stabilize whipped cream to prevent it from deflating, helps to activate the baking soda in baking, resulting in a better rise of baked goods.
Add a pinch of cream of tartar to boiling vegetables to help them retain their bright, fresh color.
Cream of tartar makes an effective non-toxic household cleaner.