Gilt was a text oriented picture editor. Now, this is easy. You can describe every picture with commands like 20 mm 20 mm 40 mm 40 mm rect . This is done by every picture editor, sometimes scrambled in a special file format, sometimes in a open format like postscript or tex-commands. They just don't show these commands until it is to late.
Gilt is different.
It shows you the picture code. It also shows you the picture and allows you to edit it with you mouse just like the other programs. Because it is text oriented it has many, up till now, unknown features. You can use all kind of text commands on your picture. Copy, paste, undo, edit all units.