meld provides a graphical alternative to the command line's diff utility; which is also covered below. meld is similar to the WinMerge application for Windows.

If you'd like to compare folders on drives, text files, binary files or folders; then meld will provide side-by-side comparisons for up to three! choices at once.

http://meldmerge.org/

A meld compare can also be started right from the command line. Here two folders are compared from the CLI. his will kick off the meld GUI and auto-start the compare.

$ meld "/media/user/5TB (external)/home/user" /home/user