TerrainEditor is a multi tool, mainly used to edit the terrain system of Falcon 4 flight sim. It offers many features, but the most important is it allows you to edit the terrain as a whole object and not in chunks.
Moreover, it offers a very easy BIN editor, where you can add, edit and remove tiles and sets from the terrain. It comes with a handy auto-update feature, which allows you to have the newest version at all times. Check the manual at the Documents section.
If you have problems right after installing TerrainEditor, take a look at the Frequently Asked Questions (FAQ) of the documentation.