[simlevesque]

  > git gui
  git: 'gui' is not a git command. See 'git --help'.
  The most similar commands are
   gc
   grep
   init
   pull
   push

[formerly_proven]

It's a separate package in some distros since it's written in Perl and uses Tk. gitk is often in the same package.

[bmn__]

Both git-gui and gitk are in Tcl, not Perl.