This is a little way of making money fast that I came up with. It depends on the assumption that if you borrow money from a bank in the morning and return it in the afternoon before the bank closes, no interest will be charged. Whether this is true I do not know, although it is an entertaining excercise nonetheless.
The name "scam" is perhaps a misnomer, since no laws are broken. However, as with any easy money method, somebody gets gypped. In this case, the victim is a faceless corporation, so you might not feel as bad about it. I'll call it a scam anyway, though, simply because it sounds cool.
The scam requires 4 participants. They will be stationed in Ukraine, New York, Hawaii, and Hong Kong. For the sake of convenience, these people will be refered to as Alice, Bob, Carol, and Dave respectively. It is assumed that in each location, the banks are open 9 to 5. The initialization of the scam requires some coordination, but it will quickly fall into a simple cycle that requires minimal effort to maintain (but you will pay dearly if ever the cycle is broken).
(Note that many large, international banks will offer loans and accounts in "world currencies" such as dollars or euros, so currency conversion will not likely be an issue.)
First, Dave in Hong Kong waits for the bank to open at 9AM, at which point he borrows an obscenely large amount of money (say, $1 billion) from the bank. He waits until 2PM Hong Kong time (9AM Ukraine time) and wires the money to Alice in Ukraine. Upon receiving the money, Alice deposits it in a savings account at the Ukrainian bank and simultaneously borrows the same amount of money from the same bank. She wires the money to Dave, who receives it well before the Hong Kong bank closes, and thus can use it to pay back his loan before any interest accumulates.
By 4PM Ukraine time, Alice is getting worried because she has a huge outstanding loan that will accumulate interest in an hour. However, she is rescued by Bob in New York, who at the same time is the first in line as the bank in New York opens at 9AM New York time. He borrows a billion dollars from said bank and immediately wires it to Alice, who pays off her loan from the Ukrainian bank just in time.
Similarly, at 3PM New York time, Bob receives a billion dollars from Carol in Hawaii, where it is 9AM and the bank has just opened. Carol has obtained the money by borrowing it from the bank. Meanwhile, Bob is able to pay off his loan, no interest charged. At 3PM Hawaii time, 24 hours have passed since the scam was initiated. Dave in Hong Kong has just awoken and is ready at the bank when it opens to borrow $1 billion from the bank, which he wires to Carol, enabling her to pay off her loan in time.
By now, you should be starting to get the hang of this. At 2PM Hong Kong time (9AM Ukraine time), Alice gets a $1 billion dollar loan from the Ukrainian bank and wires it to Dave, who pays off his own loan. And so the cycle continues.
The result of all these transactions is that 1 billion dollars is steadily accumulating interest in the Ukrainian savings account, while the corresponding debt is continuously passed around the world in such a way that no interest is ever charged on it. And all this requires no more than an hour of work every day from each of the participants.
There is a possible issue of Daylight Saving Time throwing the cycle off, which can be easily solved by interposing a fifth participant between Alice and Bob, perhaps in London. Also, you can see why any error can cause large financial losses, because if one participant is late in wiring the money, interest will accumulate on the loan, negating perhaps several weeks of scam artistry.
Finally, it is possible to terminate the cycle at any time without incurring any losses. When Dave in Hong Kong is awaiting the money from Alice in Ukraine, Alice will simply withdraw the required amount of money from the savings account rather than taking out a new loan. Thus, all debts will be paid off, and there will be some money left over in the savings account due to interest on the billion smackeroos.