Program to compare different versions of code?

I’m looking for a program that will compare, for example, two different versions of a php file and show their differences. I used to have one but I forgot what it was called and need it again.
Thanks
Answer #1
These compare php (or other languages) files to check code changes.
ExamDiff (free)
http://www.prestosoft.com/ps.asp?page=edp_examdiff
Winmerge (free)
http://winmerge.sourceforge.net/
Beyond Compare (30-day trial)
http://www.scootersoftware.com/
Links Coded. Please remember to double check that all your links have been coded -
#3.9 All links must be coded - including internal links (eg [code]Link placed inside here[/code]).
Answer #2
beyond compare is the one for me