I\'ve been wondering whether there is a good \"git export\" solution that creates a copy of a tree without the .git repository directory. There are at least thr         
        

Just use svn export.
As far as I know Github does not allow archive --remote. Although GitHub is svn compatible and they do have all git repos svn accessible so you could just use svn export like you normally would with a few adjustments to your GitHub url.
For example to export an entire repository, notice how trunk in the URL replaces master (or whatever the project's HEAD branch is set to):
svn export https://github.com/username/repo-name/trunk/
And you can export a single file or even a certain path or folder:
svn export https://github.com/username/repo-name/trunk/src/lib/folder
The HEAD branch or master branch will be available using trunk:
svn ls https://github.com/jquery/jquery/trunk
The non-HEAD branches will be accessible under /branches/:
svn ls https://github.com/jquery/jquery/branches/2.1-stable
All tags under /tags/ in the same fashion:
svn ls https://github.com/jquery/jquery/tags/2.1.3