MapBox is a suite of open source mapping tools. The MapBox Android SDK can be used to create interactive map-driven applications for Android devices. It also allows users to host their maps so that they can be embedded on webpages and shared with a wider audience.
The Google Maps API is listed as the most popular API in the ProgrammableWeb API directory. Because of its ease of use, plus the infinite possibilities for hacking together mashups, has made it the most popular API by far, way beyond the Twitter API and Youtube API.