LaTeX is always a cool tool for technical writing. And change tracking in LaTeX is awesome - you can get professional track changing output in PDF. No need to bother with bubbles in Microsoft Word. (I really don't understand why Microsoft Word tracks changes on formatting (e.g., from bold to italic). If the document is professional, then that should be a mistake fixing rather than a change because a professional document has formatting standards.)
- http://trackchanges.sourceforge.net This one even comes with a Python script that allows you to reject or accept change interactively.
- http://www.ctan.org/tex-archive/support/latexdiff/latexdiff It generates a version highlighting insertions and deleting using different colors, fonts or underlines from two LaTeX files. This one also supports put all deletions into footnotes. I would recommend this one over TrackChanges. On Ubuntu (10.04 or later), apt-get can install for you. If you just download and use on previous version of Ubuntu, you need to install Perl
- LyX: LyX is a LaTeX based WYSIWYG editor. It has GUI for tracking changes. The output can be in seen in final PDF. You can also use the GUI to accept or reject changes. I like this tool. Users don't need too much information about LaTeX. And a lotta people like GUIs.
ok, show time - well, only latexdiff.