A new GUI editor has just been added to the REVERT3D "toolkit". Now it is possible to design GUI pages using a (more or less ^^) comfortable WYSIWYG editor and save them to a file. The editor can also be configured to handle custom controls.
It has been a R3D feature since the very beginning (in fact, this was one of the first things we worked on), although we never really showed it, since there was only the "hardcoded" way to create them. The next demo versions will show this stuff and enable you to interact with GUIs using the scripting engine.