ROX-Filer generates a 'pinboard' overlay on top of this, which provides the 'grid' for where desktop icons can locate themselves. JWM defines the borders/boundaries of the desktop. Yes, it does sound odd, doesn't it what could a file manager have to do with desktop icons?)
It uses a combination of JWM - Joe's Window Manager - and the ROX-Filer file manager (think Windows Explorer. To expand on my own statement above, Puppy uses a strange way of generating its desktop.