Have some fun, thanks to PostScript and PDF programming.
Naval Battle, shown in Figure 7-13, is a PDF game in which you try to sink the computer's ships before it sinks yours. Craig Connor of Adobe Systems, Inc. created it, and you can download it from http://www.math.uakron.edu/~dpstory/acrotex.html. This site offers many other interactive PDF games, including Tic-Tac-Toe by D. P. Story.
PostScript is more than marks on a page; it is a full-fledged programming language. This means it can compute the drawing as it creates the drawing. For example, Michel Charpentier has a PostScript program that computes prime numbers (http://www.cs.unh.edu/~charpov/Programming/PostScript-primes/). Naturally, it reports its results as a printed page. If you send such a program to your PostScript printer, its interpreter actually performs the computation. If you don't have a PostScript printer or Acrobat Distiller, you can use Ghostscript to run these PostScript programs and see their results on-screen [Hack #3].
Because PostScript is a programming language, it is possible to describe large, intricate patterns using lightweight PostScript procedures. In particular, PostScript is a clever way to generate fractals (see Figure 7-11). Michel Charpentier provides good examples and a good discussion for generating (L-system) fractals at http://www.cs.unh.edu/~charpov/Programming/L-systems/. Stijn van Dongen provides another source of interesting examples at http://www.micans.org/stijn/ps/. Finally, if you are serious about mathematical PostScript, visit http://www.math.ubc.ca/~cass/graphics/text/www/ to read Bill Casselman's Mathematical Illustrations.
The PostScript web server, PS-HTTPD, is a lark on par with the RFC 1149 implementation for Linux (http://www.blug.linux.no/rfc1149/). Visit http://www.pugo.org or http://public.planetmirror.com/pub/pshttpd/ to learn more about PS-HTTPD and to download source code.