Provigil is the tradename for modafinil. Both adrafinil and modafinil are centrally acting alpha-1 agonists, which have a stimulatory effect very much like the common stimulants. Some have claimed that they don't produce the compensatory sleep debt that is inccured with many dopaminergic/noradrenergic agents like amphetamines, cocaine, etc.
Adrafinil is available through many overseas pharmacies for relatively cheap, whereas modafinil is outrageous.
Note: there is the claim of possible hepatotoxicity with both agents.