the "what's new" feature 

Newsgroups: comp.text.tex
> [...] is it possible for latex to produce "what's new" signs for the
> documents? I mean, those grey lines that goes vertically along the
> paragraphs that recently has changed?

Look at the changebar package. Also note that there is an accompanying shell script that works with diff or revision control systems to make it even easier.

Jeffrey Goldberg