A GTK twitter client using the Quickly framework and the tweepy streaming library for twitter.
It is a bit command lineish on first run, so start a terminal and put in the following commands:

sudo apt-get install bzr python-gtk2 python-gobject python-launchpad-integration python-distutils-extra desktopcouch
bzr branch lp:circleoffriends (this may tell you some stuff about informing bzr of your launchpad ID, don't worry about this, it only matters if you want to commit code changes back to launchpad)
cd circleoffriends
./bin/circleoffriends

or alternatively for a slightly bigger download and slightly less typing you can download the quickly development framework

sudo apt-get install bzr quickly
bzr branch lp:circleoffriends
cd circleoffriends
quickly run

Either way, it will then give you a URL to click on in the terminal window, click that and it will ask you to log on to twitter and allow circle of friends access to your account. Click Allow and it will give you a PIN, copy that and paste it back into the terminal and hit return. The application window should then open and follow your user stream and allow you to tweet (type in the text box, press the tweet button).
At first there will be no tweets in the window, it only follows new tweets so wait for one to happen (or tweet something).
Next time you run it the app already has your oauth credentials so will just start up. You can use edit-preferences to clear the access key and access secret if you want to go through the oauth bit again (and maybe help make it a bit more GUIish)

Bits not done yet:
* It makes no attempt to retrieve past tweets
* The "Replies" tab does nothing
* You can't reply to individual tweets
* No clicking of URLs in the tweet stream
* Support for other microblogging services
* Not particularly pretty
* Threaded conversations would be nice (quite doable, the info is there and it is a gtktreeview widget)
* The tweepy library needs to be removed from where I put it, the needed hacks have been pushed upstream so we should use that