DISCLAIMERThis is not my work. Just found and as there is no record on XDA about it, I'm just sharing the knowledge.
Nine-patch-editor @ WebLaF by Mr. Mikle Garin
The main advantages
1. Comfortable WYSIWYG editor – easily add, move, resize and remove patches
2. Mistakes-free editor – it won’t allow you to create any incorrect patches data
3. Quick preview – see all the changes you do in realtime on a small preview with custom content
4. Changes history and patches copy/paste tools included
5. Preview window can be customized with Font and Background colors (never seen before)