Currently developing a tkinter app, and loving, that I don't have to install an additional GUI framework. This will be much easier to package than with GTK or QT or Pyside or something. I am sure people have figured out all of that, but my project has so minimal dependencies, and yet offers a full GUI.

tkinter is the best kept secret in the Python std lib.

Pair it with numpy and matplotlib (two external dependencies that personally I consider part of Python itself), and you’ve got 80% of an interactive scientific simulation environment.