It is usefull tool for people who sell items on Gold and Real Money Auctions. There are many fees depending on item types, deposit funds options and currency. My calculator counts all that fees and helps you to setup right prices. Works with gold and all currency available in Diablo 3 (USD, EUR, GBP, RUB, MXN, BRL, ARS, CLP, AUD).
Ofcourse everything is online, no need download anything and it is 100% legit with Blizzard Rules.