The sensors in this coin acceptor use the thickness, diameter and fall time of the coins to identify them and it's fully programmable so you're not limited to any particular type of currency. Simply use the buttons and 7-segment display on the side of the unit to select a coin profile, insert a bunch of coin samples (or the same one, over and over) and you're good to go! After you've programmed the coin profiles, the coin acceptor will recognize them and report when each type is inserted, rejecting other coins

So maybe you won't get rich building your own vending machines but access control using different sizes of tokens might be cool, or even a virtual vending machine where you can buy MMORPG items. There are a ton of cool coin-operated projects just waiting to be built!