Diff Checker - Diff Checker is a free online diff tool that quickly and easily gives you the text differences...
Text Comparator - Compare text from two distinct sources in order to see if they perfectly match or not each other!
Beyond Compare - Beyond Compare allows you to compare files and folders.
Tkdiff - tkdiff is a graphical diff viewer based on the Tk framework.
Meld - What is Meld? Meld is a visual diff and merge tool targeted at developers.
WinMerge - WinMerge is an open source differencing and merging tool for Windows.