Trevor writes:

tgl was written a long time ago and was originally in C on Linux. It's a scripted graphics "language", although it's more of a file of commands than a language. It can do all of the usual things like load an image file, draw lines, circles and text on it and save it back out again.

tgl is almost completely superseded by ImageMagick except for a few whizzy commands which I love and use all the time like quadtoquad (which copies the pixels inside a source quadrilateral to a destination quadrilateral.) Just about anything you want to do, such as scaling, rotating, shearing, etc can be all boiled down to a single quadtoquad.

tgl is currently being upgraded with lua script for no good reason other than I like to, because really, I should be using ImageMagick too.