Side-by-side diff viewer, editor and merge preparer
tkdiff is a graphical frontend to the diff program. It provides a side-by-side view of the differences between two text files, along with several innovative features such as diff bookmarks, a graphical map of differences for quick navigation, and a facility for slicing diff regions to achieve exactly the merge output desired.
YaDT - Yet another Diff Tool. It is another front-end for diff and in earlier versions diff3 utility. With YaDT you can compare and merge 2 and/or 3 files. YaDT is written on Tcl/Tk and wrapped in a single executable file with the help of sdx and tclkit. diff and cvs utilities are embedded inside YaDT. Also, YaDT supports Git and Mercurial repositories, but git and hg are not embedded inside YaDT, you should have git/hg executable in your path environment.
Tcldiff is a Tcl extension implementing a [diff] command for Tcl scripts. It implements the options of the OpenBSD diff tool and can compare files as well as directories.