osgearth is an open-source C++ terrain SDK for creating geo-specific 3D maps with a focus on a 'no code' approach, making it accessible for both developers and non-developers. It supports various data formats and allows for extensive customization through XML map descriptions, including features like vector data styling and interactive UI elements. The SDK is well-supported, actively maintained, and can integrate with web mapping ecosystems, offering easy creation and publishing of 3D web maps.