Winmerge is a visual difference application that runs under Windows and that can be a real lifesaver in a great number of situations.
For example, if you are in a programming team and want to synchronize with other members that work on the same source files, you can easily spot the differences and merge your work, and that of the others, in a snap. The interface is very user friendly and very graphical, but after some time everyone should discover that the shortcut keys can speed even more of the workflow.
With the alt+cursor keys you can navigate and merge the differences quickly. The software supports the difference of full trees of directories and you can define filters to visualize only the files that you are interested in. For example, you can exclude the .class files if you are a java developer.
Finally, you can select the “smartness” of the difference display. For example, choosing to ignore the empty lines. On the down side WinMerge has some quirks that can be annoying. The directory difference window is a bit confused, and the version that I have tried had some problems comparing directories over a Samba connection from a Windows PC to a Sun Workstation (nothing serious fortunately). All considered, however, Winmerge is the only windows application that goes near the quality of “Meld” (Unix), and can be recommended without hesitation.