You know Google Maps!
Do you also know MapsInside?
MapsInside enables you to use your smartphone for indoor navigation. To identify your position inside a building or even outside, this innovative system calculates your position just based on wifi-signals. You can load and pinpoint your own maps and share them with your friends on the cloud. Targeting local based services as well social media MapsInside can be used also as developer API to enhance other apps with locations based information.