Diff Checker

Diff Checker is a free online diff tool that quickly and easily gives you the text differences between two files.

Free Linux Web

Tkdiff

tkdiff is a graphical diff viewer based on the Tk framework. It is capable of inter-operating with source-control systems like CVS and Subversion to show differences between a local copy and a repository version.

Free Open Source Mac OS X Windows Linux BSD Cygwin

Changes

Changes is a powerful application for comparing folders and the files they contain. Anyone who needs to see the differences between folders or files - particularly software and web developers - will find Changes useful.

Commercial Mac OS X

Ediff

Ediff is a comprehensive visual interface to Unix diff and patch utilities.

Free Open Source Windows Linux

DiffPlug

DiffPlug is a free text editor/differ and image viewer/differ. Purchasing a license allows you to diff other kinds of files such as Simulink.

Freemium Windows