GNU troff typesetting package
groff (GNU roff) is a typesetting system that reads plain text input files that include formatting commands to produce output in PostScript, PDF, HTML, or DVI formats or for display to a terminal. Formatting commands can be low-level typesetting primitives, macros from a supplied package, or user-defined macros. All three approaches can be combined.
A reimplementation and extension of the typesetter from AT&T Unix, groff is present on most POSIX systems owing to its long association with Unix manuals (including man pages). It and its predecessor are notable for their production of several best-selling software engineering texts. groff is capable of producing typographically sophisticated documents while consuming minimal system resources.