Linux
bash twitter/identi.ca ididocy, a command line client for twitter and identi.ca
Buzzbird is totally free (as in beer and freedom). There are no advertisements, and it is completely open-source. It is built on Mozilla’s XUL platform, the same technology that is used in the...
KDE Micro-Blogging Client, Currently supports Twitter.com and Identi.ca services.
Provides an omnipresent versatile search interface. It has a Twitter and identi.ca backend that let you post updates to your Twitter and/or identi.ca account.
Works with identi.ca and any other StatusNet install. Twitter dropped support for us, as oauth support is extremely unlikely.
Works with both Gnome and KDE. A launcher (inspired by Quicksilver for Mac OS) with support for sending and receiving posts to/from identi.ca and Twitter.
An Identi.ca client written in python for the n900 and other maemo devices. Also runs admirably on desktop Linux.
Hotot, is a lightweight & open source microblogging software, coding using Python language and designed for Linux.
It depends less but supports more. It's been developed actively and still in...
IdentiCurse is a simple but powerful client, primarily written for Identi.ca, but should theoretically work with any instance.
StatusNet Desktop is a dedicated multi-platform Open Source client for connecting to StatusNet installations.
Turpial is twitter client written in Python. Light, fast, fully functional and integrated to the user desktop.
Twidge is a tool for interacting with microblogging sites such as Twitter and Identi.ca. See how to use Twidge with Identi.ca.
