As it turns out, it was trivial to add support for such to ReSTedit and doing so lays the foundation for different kinds of docutils output-- HTML without CSS, PDF, etc..-- that has been on the TODO list since the project was started.
The current ReSTedit top-of-tree contains support for MarkDown. There is now a pop-up button on the toolbar that can be toggled between ReST and MarkDown. As soon as it changes, the content on the left is re-rendered using whatever markup language has been selected.
ReStructured Text seems to be a superset of MarkDown; I don't really see anything in MarkDown that can't be done in ReStructured Text nearly as conveniently. From my brief play, I'm not sure why there was a need for MarkDown as opposed to simply using docutils & ReStructured Text directly. It is quite convenient that MarkDown can produce document fragments, but it would not be hard to patch docutils to do exactly that.
In any case, if you want to build a version of ReSTedit that supports MarkDown (on Panther), then:
- download and install PyObjC 1.2
- download and install docutils 0.3.8 (package on my file sharing page)
- grab the source from here (you can mount that URL in the Finder or use 'svn checkout')
- cd into the restedit source and python setup.py py2app
The built app will be found in the dist/ directory.