I thought there was an X server for Plan 9 (edit: yes; https://plan9.io/wiki/plan9/x11_installation/index.html ), but it kinda defeats the point unless you use something like https://github.com/gerstner-hub/xwmfs on it. CDE... something like CDE probably, but actual CDE would be painful and really defeat the point unless you ported its IPC to a Plan 9 native version.