NsCDE is a retro but powerful UNIX desktop environment which resembles CDE look (and partially feel) but with a more powerful and flexible framework beneath-the-surface, more suited for 21st century unix-like and Linux systems and user requirements than original CDE.
NsCDE can be considered as a heavyweight FVWM theme on steroids, but combined with a couple other free software components and custom FVWM applications and a lot of configuration, NsCDE can be considered a lightweight hybrid desktop environment.
It also contains themes for Qt, Gtk, and more, to ensure a consistent CDE look and feel. NsCDE 2.2 has just been released, and it contains a ton of improvements. This is such a cool and fascinating project.