terrain editing tool

Can somebody recommed an open source (or at least free) terrain edition tool that can export heightmaps to png? Right now Urho3D doesnt implements terrain edition and Im needing it to create some less boring scenes.
Open source game community & development
http://forum.freegamedev.net/
rogerdv {l Wrote}:AFAIK, Blender can create terrains, but dont know if they can be exported as a heightmap.