CDE (Common Desktop Environment) is “classic” Unix desktop environment and was used in various Unix systems and OpenVMS as the default one. I also had a small experience with it in university studies (it had some Sun Solaris workstations) however I didn’t spend enough time to get used to it and have a objective opinion. KDE and Gnome projects replaced it in the most desktop environments many years ago, nevertheless CDE was open sourced in 2012 and it is actively developed since then. Last week project released 2.2.0 version of this desktop environment and besides other features/bugfixes NetBSD port was added. If you want to try it, the easiest way to do that by installing cde package from pkgsrc-wip.