Metaquokka is a highly configurable xml editor, currently available as Gridsphere portlet. Besides the default format, there is suppoert for ESysXML, a simulation description scheme for a geodynamics framework. Supports Generic Mapping Tools rudimentary.
KartoMNT is a free software of height model digitalization.
This software allows you to create your own Digital Height Models (DHM) with a simple map. Then you'll be able to visualize DHMs with the KartoMNT 3D viewer.