Kiva is a Californian website that lets you become a microinvestor. Microfinance means lending a small amount of money to people in developing countries so that they can start or grow a business. For example, I have just lent a small amount to Angin, an Armenian farmer who wishes to buy seeds and flour for her bakery and develop her farm. My contribution actually completed the $2000 she was seeking from a local loan distribution organisation as she already had 97% from other lenders. She has to repay the loan over 26 months, without interest, into my Kiva account and I can then lend it to someone else.
Kiva have a one-minute video explaining how their system works. Apparently, "100% of every dollar you lend on Kiva goes directly towards funding loans. Kiva does not take a fee, so we rely on small optional donations from you and others to keep our site running". There is no guarantee that I will get my money back, but there is apparently a 98.91% repayment rate to date.