PostScript

PostScript is the most misunderstood widely known programming language in the world. Surely widely known in the sense that, because of its enormous use, many have heard of it. And indeed misunderstood as most of them have no idea that it is a programming language at all, perceiving it as a file format for laser printers to read.

Links of Relevance:

The second and third editions of the PostScript Language Reference (‘the red book’)

Encapsulated PostScript (EPS) File Format Specification v. 3.0

PostScript Language Document Structuring Conventions (DSC) Specification v. 3.0

Various Display PostScript System (DPS) documents (DPS is also discussed in the 2nd edition of the PostScript Language Reference)

Books:: Thinking in PostScript
Mathematical Illustrations: a Manual of Geometry and PostScript (use of PostScript for producing mathematical graphics)
Practical PostScript: a small book on typesetting with PostScript
The tiny guide for PostScript markup: a book with a similar content as the above; also here

An archive of literature on PostScript from Adobe Inc, including the books PostScript Tutorial and Cookbook (‘the blue book’) and PostScript Language Program Design (‘the green book’)

Documents on PostScript fonts from Adobe Inc:: Type and type technology resources
Font technical notes (defining documents)
Adobe Glyph List: glyph names and respective Unicode code numbers