What is resveratrol used for?

No proven benefits. From studies in yeast, sirtuins (sir2 proteins) are believed to have some effects on aging, on cell death, on stress resistance (such as in situations of food scarcity), etc... Researchers are trying to find out if there are anti-aging effects in mammals. Some believe resveratrol activates a sirtuin and possibly extends lifespan, but so far research with mammals has not shown any such benefit.
Antioxidant. Resveratrol is a natural substance that comes from the dark pigment of things such as the skin of red or purple grapes and blueberries as well as peanuts. It is a type of antioxidant called a polyphenol and this is the substance that has caused all the hype about red wine. Although studies are not clear, it is thought that resveratrol may help with heart health as well as cancer prevention.