Enigmeta: Acorn scripting using Python.
"I became interested in the scripting possibilities by reading the official plugin documentation. Acorn's scripting support was meant to make new filters and such, but since it includes the PyObjC classes, you can basically do everything you can in Cocoa through Python. It's a really fast and easy way to make native Mac OS X applications, or, as in our case, extend existing ones!"
Frederik De Bleser, of NodeBox fame, is doing some awesome stuff with Acorn and Python. Make sure to watch the movie, where he adds a drawer to an Acorn window and adds new shapes and layers via some simple scripting.