Groff
Groff is the GNU replacement for the troff and nroff text formatters. It was originally written in C++ by James Clark, modelling it after ditroff, but with many extensions. The first version, 0.3.1, was released June 1990. A stable version, 1.04, was declared by November 1991.
Groff contains a large number of helper programs, preprocessors and postprocessor, like eqn, tbl, pic and soelim.
Groff is constantly being developed with new features, and is an important part of free Unix-like operating systems such as Linux and FreeBSD.
External link
de:Groff