osgEarth is Copyright © Pelican Mapping and licensed under the LGPL free open source license.
You can link to the osgEarth SDK in any commercial or non-commercial application free of charge. If you make any changes to osgEarth itself, you must make those changes available as free open source software under the LGPL license. (Typically this means contributing your changes back to the project, but it is sufficient to host them in a public GitHub clone.)
If you redistribute the osgEarth source code in any form, you must include the associated copyright notices and license information unaltered and intact.
iOS / static linking exception: The LGPL requires that anything statically linked to an LGPL library (like osgEarth) also be released under the LGPL. We grant an exception to the LGPL in this case. If you statically link osgEarth with your proprietary code, you are NOT required to release your own code under the LGPL.