History of GEM
GEM was designed in about 1984. In many ways, it was much more functional than the then-new GUI, Windows, which was released a little bit later. [Download a copy of GEM/1 from GEM World, and download a copy of Windows 1.03 from The GUI Gallery and see for yourself!].
However, GEM/1 looked too much like the Macintosh for Apple's liking. It had a trashcan and disk drives on the desktop, and a menu bar across the top of the screen with a 'Desk' menu at the left, and supported moveable, resizable, overlapping windows. So Apple took Digital Research to court and make them remove the bin and so on. The desktop now consisted of two fixed windows. GEM/2 was born. It was supplied with the AMSTRAD 1512/1640.
GEM/3 was virtually the same as GEM/2, with a new directory structure and new font/video driver formats being the main changes.
ViewMAX/1 was released a while later, which was a cut down version of GEM/3 used as the DR-DOS graphical shell. This version was supplied with DR-DOS 5, and incorporates menu shortcut keys (ALT+F for File, etc.). Support for features not needed by the desktop (fonts, the scrap directory, the Item selector) was removed or left in a state that would crash calling programs. The window gadgets in ViewMAX are based on the DOS font, not the GEM one. ViewMAX/2 was much prettier, including 3D drawing code and the ability to change dialog title colours.
ViewMAX/3 would have been the DR-DOS 7 graphical shell, but was never released. Beta code is downloadable. It was similar to Explorer/File Manager in some ways, with colour icons and directory trees.
In 1999 (I think), GEM was released as open source under the GPL by Caldera, who bought GEM and DR-DOS from Novell who bought Digital Research. The latest version is much better than the original GEM/3, with trashcans and shortcuts, Send To menus and 3D controls, background bitmaps and more.
GEM/XM and a few other versions of GEM, GEM/4, GEM/5, X/GEM, plus all the Atari versions, haven't been included. There is a version tree at Deltasoft (http://www.deltasoft.com/tree/), which offers more GEM versions.