Beyond Compare - Beyond Compare allows you to compare files and folders.
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.
Tkdiff - tkdiff is a graphical diff viewer based on the Tk framework.
Araxis Merge - Home of the award-winning Araxis Merge two and three-way file comparison (diff) and merging application, Araxis Find Duplicate Files, Araxis Replace In Files, and the Araxis Ketura issue tracking, project scheduling and time tracking application.
SmartSynchronize - SmartSynchronize - Comparing Directories the Smart Way. SmartSynchronize is a multi-platform file and directory compare tool. It allows you to compare files or perform 3-way-merges, both with the ability to edit the file contents.