Money isn't real: it's just a mutual agreement to keep track of what we've promised to each other. Frequent Flyer Miles are even less real. But trading the two, until today, could get you travel around the world at no cost.
Here's how it works. Get one of those credit cards that gets you frequent flyer points for your purchse. Then, go to the US Mint and buy dollar coins, charged to your credit card. The Mint would ship you the coins for free. You deposit the coins in your bank, pay off your credit card, and pocket the Frequent Flyer points. Voila. Something fo nothing.
Sadly, as of today the US Mint will no longer allow purchase of coins by credit card.