Navizon

Navizon is a software-only wireless positioning system that triangulates signals broadcasted from Wi-Fi access points and Cellular towers to help the users find their way in most major metropolitan areas worldwide. The Navizon network is based on a collaborative database. Members with a GPS device can use Navizon to map the Wi-Fi and cellular landscape in their neighborhoods. Once they synchronize their data, it is made available to all the other users of the network. This way, users who don't have a GPS device can benefit from a positioning system. And it's free for personal use!