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.