The zgm file extension is related to the ZenoGraphics and used for its graphics image files.
ZGM file extension - ZenoGraphics graphics image file
What is zgm file? How to open zgm files?
File type specification:
The zgm file extension is associated with the ZenoGraphics and used for its graphics image files.
The ZenoGraphics seems to be obsolete software, without any support from developers, or distributors.