BitlBee allows users to talk to people on the major instant messaging and microblogging networks (including MSN, Google Talk, AIM, and Twitter) from within any IRC client by emulating an IRC server. Virtual channels are created with all of the user's contacts in them, who can be talked to in the channel or in a query. Also, one can participate in group chats and chat rooms like they were normal IRC channels.
Qataki is a shell script that you can use to read/post notices from the command line in a simple manner. It supports Identi.ca, Twitter, and StatusNet. You can post, reply, retweet, or send direct messages; read personal, public, and user and group timelines (last statuses); read messages directed to you (i.e. where you are mentioned); read messages in context (conversations available only for Identi.ca/StatusNet); and search for notices.
PirateWall is a simple Twitter Client. It displays search results for a certain keyword or hashtag in realtime in a shell-based environment. It can also be configured to act as a data provider for many different visualization tools. For example, it is possible to use the client as a text generator for many XScreensaver applications like "apple2" or "starwars". When used in a Unix shell environment, colorized output can be generated.
Xpostulate is a blog/microblogging client that posts to Livejournal, InsaneJournal, IziBlog.net, DeadJournal, Scribbld, Inksome, Wordpress, and DreamWidth. It can tweet to twitter.com and dent to identi.ca so that you can announce new articles. This is all done via one interface, saving your login information for each, and thus simplifying cross-posting to your various social networking sites.