In its simplest form, micro-finance is the loaning of small amounts of money to people. It is usually done in developing countries in order to help fund and fuel development. Small amounts of money are loaned to entrepreneurs and paid back within a year or two, usually. Repayment rates are usually high and highest among female borrowers.
Now I will start to speculate. I think micro-finance works better than just a hand-out because the need to repay the loan pushes people to succeed. If you give someone $500, they take it and do what they will with it. If you give them $500 and require it to be repaid, they need to make sure that $500 helps them to earn at least enough money to cover the principal plus interest. Then, after the loan is repaid, they can continue to earn that money.
So, how does one get involved in micro-finance? Well, I have two suggestions:
The first is Kiva.org. It is a charity, and it accepts $25 donations and gives them to micro-finance organizations in various companies. You get to choose the loan to fund. The drawback, as far as I am concerned, is that you do not get a return on your money. You get your money back if and when the loan is repaid, but you do not earn any interest on your money. You also cannot claim your donation as a tax-deduction.
The second website is microplace.com. It is a for-profit site, and allows you to give money to support micro-finance loans. The difference from Kiva is that you do earn a return. The highest return I have seen is 5%, which is pretty low considering there is a fair amount of risk involved.
So, until micro-finance starts providing returns commesurate to its risk, it will mostly be the domain of charities. I am waiting for the day it does start returning the proper rate.