I think it was on BenjaminBrum's blog that I saw this a while ago now... Anyway, I set up an account and lent some money because I thought it was a great idea and if it didn't work out I wasn't going to be too bothered losing a few quid...
It's all explained on the website, but basically you sift through the ads and lend one or more of these guys a microloan for a business idea and they start to pay you back once they get up and running.
I lent $25 (I guess around £12.50) to a girl in Samoa in December who was looking for a loan to build a fence on a plantation. She's already made four repayments on the loan and once the repayment term is complete I can either withdraw the money or lend it to someone else, so the cash just gets recycled, which means that one loan of £12.50 can really make a difference.