ETFs (Exchange-Traded Funds) are baskets of assets like stocks, bonds, commodities…
Advantages of ETFs
LOW fees
ETFs have very low fees, compared with traditional mutual funds
DIVERSIFICATION
Some ETF replicate a whole set of indexes such as the SP500, or others global indexes,
we can also invest in commodities, bonds, specific sectors, industries, countries, or asset classes
Investing with ETF removes the risk of investing in individual asset
LIQUIDITY
ETFs are traded on stock market during the normal trading day, and in real time like any stock.
Main providers
Vanguard
You can find a lot of informations AT : http://etfdb.com/