Modafinil (brand names Modiodal, Provigil, Modavigil, Vigil, Alertec, and other) is a wakefulness-promoting agent (or eugeroic) used for treatment of wakefulness disorders such as narcolepsy, shift work sleep disorder, and excessive daytime sleepiness associated with obstructive sleep apnea.
Off-label it is used for other purposes, e.g. to treat depression, or as a smart drug (nootropic). More: en.wikipedia.org.