KDiff3 is a file and folder diff and merge tool which:
Features:
Compares and merges two or three text input files or folders,
Shows the differences line by line and character by character(!),
Provides an automatic merge-facility,
Has an editor for comfortable solving of merge-conflicts,
Provides network transparency via KIO,
Has options to highlight or hide changes in white-space or comments,
Supports Unicode, UTF-8 and other file encodings,
Prints differences,
Supports version control keyword and history merging.
What’s new in version 1.12
Completed port away from Qt5. Qt6.6 now required version due to delayed ICU support in Qt.
Fixed UTF-8-BOM output encoding issues, mostly seen on Windows.
Horizontal scroll correctly comptuted for diff windows. Note due to changes in windows/Qt the scrollbars may be vary small or hidden on Windows 11. This cann't be controlled from kdiff3.
False errors on first launch with files selected should be fixed.
I tried KDiff3 some time ago, so maybe they made some progress in the meantime, but it was painfully slow compared to VisualDiffer, which weighs only 3.7 MB. On the positive side, KDiff3 is free and should work in 10.9+.