Resveratrol is the beneficial compound found in red wine that is associated with life extension and some of the health benefits in wine. It is produced in grapes as a defense against toxins, and is contained in the skins.
It is most well known for supposedly increasing lifespan, and it might. It does not have a novel and unique mechanism for increasing lifespan in humans, although it does in some research animals (Drosophilia). It can, however, protect humans from heart disease and insulin resistance and may extend life by that mechanism. This is more of a 'adding life to years' action than an 'adding years to life' mechanism.
It also shares a lot of beneficial effects with many bioflavonoids, such as reducing the occurrence of osteoporosis, beneficially influencing fat cell production (in favor of long-term fat loss) and modulating blood pressure; usually a reduction of blood pressure.