Scripts and libraries

Applescript 

• ASTwitterLibrary 1.1 - Integrate Twitter into your Applescripts or Applescript Studio project.
• iTwitStatus is a way to use your Twitter as your iChat Status via QuickSilver.
•  | Tweet - update Twitter via Quicksilver
• TwitterAdium by Jesse Newland
• TwiTunes is an AppleScript for Mac OS X that posts the current iTunes track to Twitter: "Linda is listening to "Take on me" by A-ha." Can be customized easily.
• iQuickTwitter - My Quicksilver + Twitter + iChat + Growl Hack: An AppleScript that integrates Quicksilver, iChat, and Growl with Twitter.
• Growlified Tweet Deluxe (based on Ted Leung's Growlified Tweet) is a Quicksilver AppleScript action that uses Growl and checks message length before posting.
• Qurl for Twitterrific. Applescript to convert URLs to Qurls. By Greg Fischer. More info here (UPDATED. No longer dependent on secondary scripts)

BASH shell 

• Twitter using BASH and cURL on a Mac Terminal line - should work with any OS that supports BASH and cURL
• Parses BBC rss feeds and pipes them to Twitter using cURL - in BASH, by Guillaume Riflet.
• Display Tweets using notification daemon (Gnome, etc) - in BASH, should work in any disto with notify-send.
• Post /w BASH+cURL + Spell Check + Length Check - More stuff on top of the script above.

Jabber 

• Jabber::Simple (src, doc) is a simple (duh!) Ruby library that aims to make the implementation of basic Jabber functionality trivial
• TwitterPated is a script to interact with Twitter via Jabber to make it simpler for multiple people to publish to a Twitter identity.

Java 

• JTwitter is a simple Java interface to Twitter. It provides nice Java methods and objects for accessing Twitter.
• Twitter taglib - access to Twitter right from your JSP (or Coldfusion) pages

JavaScript

• TwitterJS easy to implement JavaScript twitter badge with lots of options to customise appearance.

Perl 

• Perl command line tool for setting twitter status by Shantanu Goel
• Perl command line tool for direct messages by Stephane Kattoor
• wd - a perl script to get/set twitter status from the command line. Source.
• Twitish A twitter shell written in Perl for Linux and *nix.
• How to hook twitter into a IRC channel by Harper Reed
• Email to Twitter by Leonid Mamchenkov
• Updating Twitter from irssi by John Anderson
• Reading and updating Twitter from irssi (with Ping.fm support) by Remco Brink

CPAN Modules 

• Net::Twitter by Chris Thompson (Debian Package, relies upon libjson-perl)
• Twitter::Shell by Daisuke Maki
  • twitter shell
• POE::Component::Client::Twitter by Kazuhiro Osawa
  • twitter irc gateway

Movable Type 

• MT-Twitter An easy way to announce Movable Type blog posts via Twitter. From Chopstix Media.

PHP 

• Syndicate Twitter to your blog by David Kadavy
• RSS to Twitter by Paul Stamatiou
• MailTwitterPHP is an email to Twitter gateway script that attempts to connect to a specified IMAP inbox, cycle through all email and attempt to post the body of each email as a new Twitter to a specified Twitter account. Requires a PHP install with IMAP support compiled in.
• Twitter + PHP Update your Twitter status from within your PHP scripts
• Twitter2HTML Show your latest tweets on your website with this simple PHP script. (via API, not RSS for instant updates. Requires cURL.)
• TwitterSig Show your latest tweet in an image file for use in forum sigs, etc. Requires PHP5.)
• PHP code from scratch to get the user updates and display it on your page the way you want.

TYPO3 

• timtab_twitter by Frank Nägler aka NeoBlack (announcement)
• fn_lib contains a PHP twitter client by Frank Nägler aka NeoBlack (announcement)

Drupal 

• Twitter Module for Drupal by James Walker aka Walkah (announcement) automatically sends updates when new content is added
• Send Twitters from Drupal - a simple form for sending a twitter message by kaerast
• Twitter Direct Message on new comments in Drupal - get a twitter direct message everytime someone submits a comment baramunchies

Ruby

• Safaritweet - Posts the title and URL of the currently active Safari tab on Twitter, hashtags can be passed in as command line parameters. Uses RubyOSA for AppleScript magic, twitter4r and ShortURL.