Gem was the graphical interface provided with the Amstrad PC 1640 and 1512 computers, even being XT class computers it was great to have a mouse and graphical interface.
Now actual information about GEM can be located on this link:

To download GEM and know about the history try:
gem green disk
This is the third disk (green one) spanish version

This is a cool tiger image shown on all manuals

gem disks
The four disks

amstrad PC 1512
Amstrad 1512 with the four disks and manual.