I have created a basic terrain editor that integrates with the Urho3d Editor. This is in very early stages and is only about two days worth of work. It currently supports raising/lowering terrain, setting the height of the terrain, and smoothing the terrain. This is all done using "Brushes", which you can create and edit. Terrains are saved to the file they we're loaded from, and editing one will cause SetSceneModified to be called (therefore prompting you to save before exiting). This is WIP and should not be considered done in any means.