Both Gnome Flashback and Gnome Classic are what you get when you install Gnome Shell Extensions on Gnome. They are both desktops and Gnome Flashback can be run on it's own as the only desktop without Gnome. While Gnome Classic can't be. Here I take a look at both.
This is a good alternative for users coming from Windows who want a light desktop. Gnome Flashback is very light. It can run on laptops with low hardware.