Boston based Loki has released the a software-only positioning system that leverages a nationwide database of known Wi-Fi access points to calculate the precise location of any Wi-Fi enabled device.  

According to Loki’s website, the service utilizes the web (via WiFi) to identify your exact physical location, then lets you easily find the nearest jazz club, directions to the cloest Thai restaurant, cheapest gas prices in town, etc.

Sounds like it could be an interesting option in dense urban environments where getting a clear GPS signal is more difficult than WiFi. Check it out HERE