From Scott Hansen's Internetbusiness Review Site:
What This Amazing Software Does:
Compares two articles side by side and reveal to you the percentage of duplicated content between the two articles.
Shows you exactly which are the parts that are duplicated using different color highlighting.
Saves you time and effort when rewriting articles due to the easy comparison.
Displays the keyword density of each article for the keyword you've chosen.
Helps to check on your freelance writers work and ensure all your content are not duplicated and will never be penalized by the search engines.