GNU Source-highlight produces a document with syntax highlighting when given a source file. It handles many languages, e.g., Java, C/C++, Prolog, Perl, PHP3, Python, Flex, HTML, and other formats, e.g., ChangeLog and log files, as source languages and HTML, XHTML, DocBook, ANSI color escapes, LaTeX, and Texinfo as output formats. Input and output formats can be specified with a regular expression-oriented syntax.
The Heirloom Documentation Tools provide troff, nroff, and related utilities to format manual pages and other documents for output on terminals and printers. They are portable and enhanced versions of the respective OpenSolaris utilities, which descend from ditroff and the historical Unix troff. troff provides advanced typographical features such as kerning, tracking, and hanging characters. It can access PostScript Type 1, OpenType, and TrueType fonts directly. Internationalized hyphenation, international paper sizes, and UTF-8 input are supported.
OmegaT is a translation memory application intended for professional translators. It does not translate for you (software that does this is called "machine translation"). It features fuzzy matching, match propagation, simultaneous processing of multiple-file projects, simultaneous use of multiple translation memories, and external glossaries. Document file formats include plain text, HTML, and OpenOffice.org/StarOffice. It has Unicode (UTF-8) support (can be used with non-Latin alphabets). It is compatible with other translation memory applications (TMX Level 1).
Aephea is a text-based authoring tool for HTML. It enforces well-formedness with a simpler and stricter TeX-like syntax and provides useful extensions and abstractions with facilities for adding new ones. It emphasizes a single unified approach that stays close to HTML itself and promotes and utilizes CSS extensively. Abstractions such as dictionary stacks, arithmetic, and iteration are part of Aephea.
deplate converts wiki-like markup to LaTeX (standard classes, koma, dramatist, sweave), HTML/PHP (single page, chunked/website, HTML, or s5-based slideshow), DocBook (article, book, man/ref page), and really plain text. Currently supported input formats are viki and Ruby's rdoc. The viki markup supports footnotes, citations, index, table of contents, embedded LaTeX for mathematics, integration with R for dynamically generated figures and tables, and more. Output can be customized via page templates.