PyGtk is a set of Python bindings to the popular GTK Toolkit. It provides an object-oriented interface that is slightly higher level than the C one. It is simple to install on Unix, Win32 installer versions are available, and Mac OS X versions are in development.
KiWi is a set of classes and wrappers for PyGTK that were developed to provide a sort of framework for applications. Roughly modelled on Smalltalk's MVC, Kiwi intention is becoming a simple way to make a UI.
Note: New users are encouraged to use GTK+3 through the PyGObject bindings instead of using PyGTK with GTK+2. Windows users may still want to keep using PyGTK until more convenient installers are published.