Hi Greg,
Still, TeX has one significant advantage over [gt]roff
that I'm aware
of: it adjusts paragraphs, not lines, and it seems that in some cases
this give better looking layout.
Gunnar Ritter's Hierloom troff, a descendent of OpenSolaris's, can
adjust paragraphs rather than lines.
http://heirloom.sourceforge.net/doctools.html
Ali Gholami Rudi's neatroff, a troff re-implementation, adjusts
paragraphs. Search for `paragraph-at-once' at
http://litcave.rudi.ir/
or
http://litcave.rudi.ir/neatroff.pdf
There could be others.
--
Cheers, Ralph.
https://plus.google.com/+RalphCorderoy