Hrafn is a python twitter application. It started because no existing client supported the Lists API, but has grown to be a general-purpose Twitter client.
Just run ./hrafn.py, and start playing around. Right now, it is best to run this file in-place; it expects all the .py files and default.glade to be in the same directory.
To register an account with hrafn, simply click File -> Add Account. An authorization screen will launch in your web browser. When you finish there, you should have a PIN. Copy this into the popup that hrafn created, and click 'ok'.