Unroff is a Scheme-based, programmable, extensible troff translator
with a back-end for the Hypertext Markup Language.

Unroff reads and parses UNIX troff documents and translates the embedded
markup into a different format.  Neither the actual output format nor
any knowledge about particular troff macro sets (-man, -ms, etc.) are
hard-wired into unroff.  Instead, the translation process is controlled
by a set of user-supplied procedures written in the Scheme programming
language.

Translation rules for new output formats and troff macro packages can
be added easily by providing a corresponding set of Scheme procedures
(a `back-end').  Version 1.0 of unroff includes back-ends for translating
documents using the `man' and `ms' macros into the Hypertext Markup
Language (HTML) version 2.0.  Additional requests facilitate use of
arbitrary hypertext links in troff documents.

WWW: https://www-rn.informatik.uni-bremen.de/software/unroff/