Every single business following the HYIP model has turned out to be a ponzi scam.

I would think that a "legitimate" HYIP would be possible however. Think of the real estate business. If you have a rental property as an investment, it is possible to make a 8-15 percent annual profit. A business could buy a property and sell shares in the property which would return a weekly, monthly, or yearly profit. Shares could be resold once bought, hence leaving your initial investment intact.

There are also professional stock and forex traders who are able to earn a living by trading in these markets. A business could be set up that allows people to pool their investments together into a single fund. Successful traders would be given the option of using the funds in this pool in addition to their normal funds, and if they choose to do so, they would be entitled to a percentage of their profits. Therefore, a trader who has $100,000 of his own funds and normally makes $50,000 a year would be able to gain access to $1,000,000 of investors' funds and make an additional $500,000 a year. Even if he was entitled to just 10 percent of profits, the trader would now be making $100,000 a year and the investors would get $450,000. Everyone wins.

Finally, there is also an opportunity to profit by giving out loans. This includes mortgage loans. A business could be set up that allows investors to pool their money together and give out loans. The profits would come from the interest that is paid once the loan is repaid.

I can think of other business models that might be able to pool investors' funds and give out the profits in a weekly, monthly, or yearly manner. Life insurance, for example.

Got any other ideas?