GEM was in fact developed by DR (Digita Research) and when DR got
bought by Caldera, it became free software. Not "open source for
non-commercial use" like CP/M or DR-DOS, but actual GPL software.
Consequently, it has been developed into just about the best GUI you
can throw onto a 286 and have work. See the latest version of the
leading distro here:
http://gem.shaneland.co.uk/opengem5core.html