Skobbler uses the free editable OpenStreetMap to create apps such as GPS Navigation 2, and ForeverMap that provides maps offline that work when you can't be online. The company has just released the Skobbler tiles API. Compatible with popular frameworks like Leaflet, OpenLayers and Google Maps API v3, its API allows you access to its tile server and to embed maps in your applications.
Have you noticed the many tools to share your location? There's FourSquare and Gowalla, both about a year old. Then there are old-timers like Brightkite. And now, there's one that works with all three (and a couple more).