Meld is an open source visual diff tool.
Meld helps you compare files, directories, and version controlled projects. It provides two- and three-way comparison of both files and directories, and has support for many popular version control systems.
The primary purpose/intent is for comparing code, such as in this screenshot,
I use it for several reports where I receive monthly text dumps and need to update various Word and PDF documents with any changes. Meld turned what used to be an hours-long process for another group into something that I can typically turn around in about 10 minutes.
The only caveat is that Meld only works with text files for file comparisons like this. If you need to compare Word or other documents, you’ll need a different tool.