OpenLayers
A high-performance, feature-packed library for all your mapping needs
...It is completely free, Open Source JavaScript, released under the 2-clause BSD License (also known as the FreeBSD). Pull tiles from OSM, Bing, MapBox, Stamen, and any other XYZ source you can find. OGC mapping services and untiled layers also supported. Render vector data from GeoJSON, TopoJSON, KML, GML, Mapbox vector tiles, and other formats. Leverages Canvas 2D, WebGL, and all the latest greatness from HTML5. Mobile support out of the box. Build lightweight custom profiles with just the components you need. Style your map controls with straight-forward CSS. Hook into different levels of the API or use 3rd party libraries to customize and extend functionality.