From Wikipedia:

“The Common Desktop Environment (CDE) is a desktop environment for Unix and OpenVMS, based on the Motif widget toolkit. It was part of the UNIX98 Workstation Product Standard, and was long the “classic” Unix desktop associated with commercial Unix workstations.

After a long history as proprietary software, CDE was released as free software on 6 August 2012, under the GNU Lesser General Public License, version 2 or later. Since its release as free software, CDE has been ported to the Linux and BSD derivatives.”

 sudo apt-get install cde-desktop

CDE can be also installed via APTus, MinimalGUI/CLI ISO image or the 'sparky-desktop-cde' meta package.