TweetDeck - TweetDeck is your personal browser for staying in touch with what’s happening now.
Gwibber - Gwibber is an open source microblogging client for GNOME developed with Python and GTK.
Twitterfall - Twitterfall is an excellent choice if you want something basic, free and without much branding.
Choqok - Choqok - KDE Micro-Blogging Client The name comes from an ancient Persian word, means Sparrow!
Tweetdeckr - Tweetdeckr is an open source Tweetdeck replacement client.
Seesmic - Seesmic was a suite of freeware web, mobile, and desktop applications which allowed users to simultaneously manage user accounts for multiple social networks, such as Facebook and Twitter.