I love great ideas and FON is really one of them. Founded in the year 2005 by the Argentinean entrepreneur Martin Varsavsky in Madrid (Spain) has as a main objective to create the largest Wifi Network in the world, and gosh, they are doing it! They already have more than 11 million wifi hotspots worldwide.
How they do it?
You have to get a Wireless access point from FON (they called them Foneras) and by connecting it to your own router the Fonera will share a little bit of your Internet connection with the FON network. This way a person that could reach the Fonera range at your house could connect to the internet thanks to you. The concept is really easy, they create a separate network to ensure nobody would have access to your local network, and if you share your internet connection with a FON access point you will be able to use the whole worldwide FON network in exchange.