KDiff3 is a file and folder diff and merge tool which

• 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.