Few of Google’s projects, rumors of projects, and acquisitions have generated as much envy among Linux users as Google Earth. In some respects the search engine behemoth is quite OS-agnostic, but the 3D virtual globe remains limited to Windows desktops. But there is an alternative: NASA’s World Wind project. Like Google Earth, it’s a 3D planetary visualization system that overlays satellite imagery, weather, political, and topological map data. The difference is: World Wind is open source.