1. The diff command compares files line by line. Diffstat reads theoutput of the diff command and displays a histogram of the insertions, deletions, and modifications in each file. Diffstat is commonly used to provide a summary of the changes in large, complex patch files. Install diffstat if you need a program which provides a summary of the diff command's output. You also need to install diffutils. From Redhat 8.0 RPM

2. produces graph of changes introduced by a diff file This program is a simple that reads the output of the 'diff' program, and produces a histogram of the total number of lines that were changed. It is useful for scanning a patch file to see which files were changed. From Debian 3.0r0 APT