Wikipedia
OpenGEM
OpenGEM is a non- multitasking 16-bit graphical user interface (GUI) for DOS. It is an extended distribution of FreeGEM that includes features of the original Digital Research GEM.
OpenGEM is intended to provide a simple to install and use GUI system and windowing framework for the FreeDOS operating system.
OpenGEM was developed by Shane Coughlan in collaboration with the FreeGEM Developer team, and is free software released under the terms of the GNU General Public License (GPL). OpenGEM versions 3 through 6 are hosted on SourceForge and on the FreeDOS website.
OpenGEM has not been actively developed since 2008 but is feature-complete as a basic GUI and includes a full SDK for future third party development or extension.