KDiff3 - file & directory diff and merge tool

KDiff3 is a program that:

compares or merges two or three text input files or directories,

shows the differences line by line and character by character (!),

provides an automatic merge-facility and

an integrated editor for comfortable solving of merge-conflicts,

supports Unicode, UTF-8 and other codecs, autodetection via byte-order-mark "BOM"

supports KIO on KDE (allows accessing ftp, sftp, fish, smb etc.),

Printing of differences,

Manual alignment of lines,

Automatic merging of version control history ($Log$),

and has an intuitive graphical user interface.

Windows-Explorer integration Diff-Ext-for-KDiff3 - shell extension included in installer (originally by Sergey Zorin: see also Diff Ext)

KDE-Konqueror service menu plugin

Simplified integration with IBM-Rational-Clearcase for Windows

Read what else is special in a short abstract (PDF).