WinMerge

WinMerge is an Open Source differencing and merging tool for Windows. Use it to detect changes between files and folders, and then to merge changes selectively. You can use WinMerge by itself, or launch it from a version control system or another application.

When you compare two files or folders, the result is displayed in the WinMerge window. The WinMerge window's visual display and functions are designed to help you see differences between your targets, and to merge selected differences if you want to.

In a file comparison: WinMerge shows differences between lines. The built-in text editor provides syntax highlighting for several programming languages and other file formats.

In a folder comparison: WinMerge indicates various kinds of differences between the files that the folders contain.