Reimplementations
- groff is GNU Project's free replacement for troff and nroff.
- unroff is an extensible replacement of troff written in Scheme
- Heirloom troff is based on troff from OpenSolaris. It includes support for OpenType fonts, improved support for Type 1 fonts, support for Unicode, a new paragraph formatting algorithm, and a groff compatibility mode.
- mandoc is a specialised compiler/formatter only for the man and mdoc macro packages.
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