gnome-directory-thumbnailer
About
gnome-directory-thumbnailer is a GNOME thumbnailer utility which will generate a thumbnail for a directory. It is intended to be called by gnome-desktop’s thumbnailer code, but can be called manually as well.
gnome-directory-thumbnailer was first developed in October 2013: http://tecnocode.co.uk/2013/10/21/writing-a-gnome-thumbnailer/.
Bugs
Bugs should be filed in the issue tracker.