Meld
Being free and open source, Meld is a very popular tool on Windows (it's also available for Linux). It supports three-way comparing and merging and lets you edit files directly from the comparison view. Apart from diffing files, Meld also supports comparison of folders.
DiffPDF can compare two PDF files. It offers three comparison modes: Words, Characters, and Appearance. By default the comparison is of the words on each pair.
Beyond Compare
Tiny date, time diff calculator. There are times you want to check how old you are (in years. Until I can fix this you might want to try Diff Ext by Sergey Zorin. 2009-03-25: Mac binary available for version 0.9.95 (created by Michael Schmidt) 2009-03-03: Version 0.9.95. Show line end style for each file. Translation update. For the complete list of changes see the ChangeLog and the Release Message and MD5-sums. WinMerge is an Open Source differencing and merging tool for Windows. WinMerge can compare both folders and files, presenting differences in a visual text format that is easy to understand and handle. Much like Araxis, the DeltaWalker diff tool also lets you compare office files.However, it goes one step further by letting you compare file archives like ZIP, JAR, and TAR files. If you're regularly performing comparisons on a folder basis, it's good to know that DeltaWalker shines with great performance in this area.
The Beyond Compare team makes a fine diff tool for Windows (as well as macOS and Linux, by the way). It goes well beyond (pun intended) diffing simple text and also allows comparing PDF, Excel and image files. The 'Pro' version also includes a solid three-way merge.
Araxis Merge
Just like Beyond Compare, Araxis Merge supports more than just text and image files. It also lets you compare office documents (like MS Word, Excel, Powerpoint, or ODF). It comes in standard and professional editions, and for people working on both Windows and macOS, it's good to know that a single license is valid for both platforms.
KDiff3
Another free and open source tool answers to the name of KDiff3. The project hasn't seen many updates in recent years (though you may be able to find more recent releases through this page), but it remains a solid diff and merge tool that should satisfy basic needs.
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DeltaWalker
Much like Araxis, the DeltaWalker diff tool also lets you compare office files. However, it goes one step further by letting you compare file archives like ZIP, JAR, and TAR files. If you're regularly performing comparisons on a folder basis, it's good to know that DeltaWalker shines with great performance in this area. DeltaWalker supports Windows, macOS and Linux.
P4Merge
Perforce, the company best known for its enterprise version control platform, also offers a solid diff tool: P4Merge is free of charge and comes with a basic feature set that makes it an interesting option on Windows, macOS and Linux.
Code Compare
Besides offering all the standard diff and merge capabilities, Code Compare comes with some special features like syntax highlighting, semantic code comparison and a VisualStudio integration.
The basic version can be used free of charge, while the Professional Edition delivers the full feature set.
WinMerge
WinMerge is an open-source diff tool with some nice features like folder and image comparison, and three-way file comparison.
Guiffy
Guiffy is a full-featured tool with syntax highlighting, three-way comparisons and merges, and multiple comparison algorithms. It comes in pro and expert versions, and supports Windows, macOS and Linux.
Integrations
Another aspect to watch out for is integrations: before choosing your favorite tool, you should make sure that it plays nicely with the rest of your tool chain. I can already confirm that most of the mentioned tools work seamlessly with Tower, our own Git client.
If you don't need the power of a dedicated Diff tool application, the integrated diff views in Tower might even be sufficient for you:
See for yourself and try it 30 days for free.
Conclusion
Diff & merge apps are amongst the most underestimated tools. But a good one can be really helpful in a lot of situations. Try one of the above and see for yourself!
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