A TWENTY-one-year-old university graduate has become the recipient of the world's largest early investment funding for a mobile payment app that isn't yet publicly available.

The Stanford graduate, Lucas Duplan raised $25 million in funding for his app, Clinkle. What the app actually does, nobody really knows. It hasn't launched yet.

The Clinkle website says it is "rebuilding your analog wallet from the ground up to bring you the future of payment."

Duplan is keeping mum about what it actually does.

"Our goal is to completely modernise how payments work," Duplan told Business Insider. "What we're trying to do is basically take your phone and have it for the first time be able to rival cash and credit cards. We've developed a way for consumers to download an app, no hardware needed, and achieve scale from a software point of view."

Duplan grew up in California and it seems he has always had a knack for business. He first started making money as a teenager by selling iPod cases on eBay. He also rented out his parents' wireless internet connection in Croatia - where they are originally from.

In 2010 at the tender age of 19, Duplan enrolled in a study abroad program between his freshman and sophomore year at Stanford University.

He said he was inspired to create his app "Clinkle", after having to carry around piles of coins instead of the notes he was used to using in the US. In fact the app is named after the "clinking" sound the coins made, he told the Wall Street Journal.

He said he was annoyed that he could use a mobile phone or computer to post a comment on Facebook or send an email free of charge, but that trying to do it with money - which he said was "just another form of data" - was much more difficult.

A virtual wallet would mitigate the need to even carry around credit cards, let alone cash.

Duplan has a huge challenge ahead of him, when his app eventually launches for Apple and Android devices later in the year he will be taking on the likes of Google and PayPal who both have their own online payment services.

Still, he must be doing something right, companies like Intel, former Facebook COO, Owen Van Natta and wireless technology company Qualcomm (among many others) have all invested their money and faith in him.