A specialized Mutual Fund. Many not available to US citizens, or only to those who have lots of money to lose. They attempt to use multiple types of securities (e.g. equities vs futures) to reduce risk. But sometimes the opposite happens.
The most famous Hedge Fund-s are probably
the Hedge Fund Association http://www.thehfa.org/ Many, but not all, hedge fund strategies tend to hedge against downturns in the markets being traded. Hedge funds are flexible in their investment options (can use short selling, leverage, derivatives such as puts, calls, options, futures, etc.). Hedge funds benefit by heavily weighting hedge fund managers' remuneration towards performance incentives, thus attracting the best brains in the investment business.
http://www.hedgefundcenter.com/ includes aggregator of YahooNews