Free GPL (GNU GENERAL PUBLIC LICENSE).
Ranked in these QuestionsQuestion Ranking
Pro Supports 3 way merges
For modern version control systems, 3way merge support is a basic requirement, but many other open source diff viewers do not adequately handle 3way merges.
Pro Free and open source
KDiff3 is completely free to download and use. It's also open source released under the GPL.
Pro Can compare directories
It is able to compare whole directory trees.
Pro Supports editing files directly
In addition to comparing two files it also allows you to edit the merge result right in place.
Pro Diff by character not by lines
On comparing two files, difference is shown by characters; not by lines.
Pro The UI is customizable
Allow customizing colors regardless of user/system theme.
Pro Supports manual code aligning
With selecting code in one window and hitting Ctrl+Y, then selecting some other code in second window and also hitting Ctrl+Y you can manually align the code.
Pro Preprocessing before calculating differences
There are options that may pre-process compared files before Kdiff3 actually do a comparison - to ignore for example automatically generated dates and/or revision numbers added by commit hooks.
Pro Context menu shortcut
You can right-click a folder/file and the options:
- Save <file> for later
- Compare with
will be available, making launching KDiff3 really convenient.
Con Cannot do inline diffs
Comparison of 2 files is always side-by-side and there's no option for inline views. Overall a rather poor and confusing UI in general.
Con Confusing GUI
4 sub-windows (when you really only need 3), a lot of different colors and even more confusing result-window. No links what has changed between versions and and the result. It clearly shows it's dated or rather outdated. Great if you ever need to do a command line merge, otherwise it sucks.
Con No precise editing of the compared files
Precise work line-after-line is not possible. Only a version after the automated merge-step is editable, but not the two files separately.
Con No longer supported by Homebrew for MacOS
Cannot be installed easily on Mac as of Aug 2019.
Con Problems when files have different number of lines
For example, if you add 3 lines: A, B and C locally but on the other change there are only A and C, Kdiff3 will work out that A was added, then it says that B conflicts with C but adds C again anyway.
Con Slow for large files
Con No image compare
Compare is text based.