There isn't one.
All authoring freeware is either:
- Based on the Linux software "DVDAuthor" and is not easy to use.
- Part of an all-in-one like DVD Flick, meaning it may re-encode (and therefore reduce quality) of your video/audio assets. (There's also well-documented issues with losing audio/video sync with most of these types of programs, including the freeware DVD Flick.)
One program I've not yet had time to try is Bombono:
http://www.bombono.org/cgi-bin/wiki/
It may work, it may not. Not idea how hard or easy it is to use.
If I had to guess, I'd say it likely is as difficult as the DVDAuthor GUIs, and may have common sync errors. (Would be nice to be wrong.)
TMPGEnc DVD Author (aka Authoring Works) and Ulead DVD Workshop 2 are the easiest authoring programs. Of course, neither are free, and DVDWS2 isn't sold anymore.