PostScript is a program developed by Adobe Systems
that Apple used in its first laser printers. The founders
of Adobe were Chuck Geschke and John Warnock. Geschke
taught calculus at Rochester University for a while
before he figured there had to be a faster
and less boring way to get rich.
One virtue of PostScript is that PostScript files
are easily accessible in TEX.
Popular programs like xfig or PSTricks output to PS.
but it is usually better to program directly in PS.
For heavy work,
write programs in Java or C that output to PS.