NaturalGUI .Net Edition is an open-source front-end for Natural Docs in .Net, written by Daniel Aguilar.
You can download Beta 4 (13K) from Daniel’s site and read his latest blog post on it.
With this last version you can save “.ndc” files containing your gui settings for later use.
There’s also a page dedicated to NaturalGui.
See also: NaturalGui Java Edition by Richard Leggert, Natural Docs.