TCL/TK is incredibly powerful to put a GUI in front of a bunch of scripts. You can easily bind a regexp in a log file to events that update widgets. I wish I had learned it 20 years ago.
If by "that" you mean an example of a GUI on top of scripts, the `git gui` and `gitk` that ship with git are in Tcl/Tk and shell out to the git commands that do the work
As others have mentioned, they are very, very not "native UI" friendly - OSX is an especially bad instance - but they do run on all of Git's platforms without a 20MB runtime to go along with them. If Tk's widgets were just a little less harsh, those two would absolutely be my go-to graphical git clients.
