• BigTweet - BigTweet installs as a bookmarklet and allows you to post to Twitter from any web page. Choose a classic 140 character update, or a 240 character tweet. Insert special Unicode characters and shorten URLs with the Bit.ly API right from the bookmarklet window. Automatically capture the current page title, URL and any highlighted text. No registration is required - only Twitter login credentials are needed.
  • Flock - A social Web Browser that has twitter integration built in.  Flock also integrates many other social networking services.
  • Book Price Check - a simple way to check book prices via reply and direct message to your mobile device.
  • Search Cloudlet - is an easy-to-use Firefox add-on that inserts context-aware tag clouds into a traditional Google, Yahoo and Twitter interface to help you navigate more efficiently through search results.
  • Twitterfox - TwitterFox is a Firefox extension that notifies you of your friends’ tweets on Twitter. This extension adds a tiny icon on the status bar which notifies you when your friends update their tweets. Also it has a small text input field to update your tweets.
  • AlertThingy - AlertThingy v2 brings the very latest updates from your favourite social networks direct to your desktop. Plus send Tweets, update your Facebook status, upload photos to Flickr, post to Tumblr and more. With v2 AlertThingy makes it faster and easier to manage the online you. Plus you get the coolest looking RSS reader on the interweb.
  • Friendbar- A Firefox toolbar that is the best way to follow Twitter & Facebook updates, and post to Twitter and Facebook
  • twAitter (Now in Alpha) - A full Twitter web client with a comprehensive scheduling platform.  Schedule tweets to send at anytime(recurring included).  Manage your scheduled messages with an Outlook style Twitter Calendar. (www.twAitter.com)
  • Twitterified - A fast client that also allows users to send/view long messages, pictures, and embedded documents.
  • Tweetree.com - Web based interface for viewing your twitter stream in a tree with replies nested under the original post they were in reply to. Also pulls in external content from Twitpic, YouTube, etc and displays in right in your feed so you don’t have to click through every link to see what it is.
  • Mibbit.com - A web based IRC, Yahoo and Twitter client.
  • mytweet16.com - a web app that lets you view any users first 16 tweets. Also has a list of the top 16 searched for users.
  • gtwit - a web based twitter client which works in all modern browsers without any plugins that supports smart completion, history and personal search of your tweets by storing them on Google’s cloud
  • TwitterGadget - iGoogle gadget and/or browser-based auto-refreshing twitter client with clean web-2.0 style interface and many user configurable options.
  • Tw-autocomplete - Firefox extension to add autocomplete on Twitter.com for @-messages and d-messages
  • Autocompletter - lightweight Greasemonkey script to add as-you-type autocomplete for @ usernames on Twitter (demo).
  • Ear2Ground - Now Ear2Web. An Adobe AIR application that provides live coverage of tweets in your geographic area! Optionally follow tweets on a specific topic in your area.
  • Yoono - Receive alerts, update your status or message your friends in your browser sidebar. No need to switch from one site to another or from your browser to a desktop app anymore. The perfect tool to become a twitter heavy user without spending hours on it. Yoono also integrates many other services : facebook, flickr, friendfeed, major IM services
  • Shareaholic for Firefox - easy and quick way to post URLs to Twitter from within your browser. Grand Prize winner of Extend Firefox 2, a Mozilla sponsored contest for the best Firefox addons.
  • Statuzer a multi-account twitter client with music tweets support (song.ly tra.kz)
  • TwitKit Integrate Twitter into your Firefox browsing experience.
  • TwitterBack Sync and befriend all of your followers.
  • Post to Twitter from Vim for Vim users.
  • Twitter Opera widget A widget for the Opera browser.
  • TTYtter An interactive text-mode Twitter client, with full background asynchronous updates, written in Perl 5. Requires curl or Lynx, but no additional Perl modules. Tested on Mac OS X, NetBSD, AIX and other Unix-like OSes. Includes full API and a “bot” daemon mode.
  • Nitwit, the cross-platform microblogging client for Twitter, Jaiku and other platforms including Jabber and IRC. Written in PHP-GTK.
  • Tweetr one of the best twitter desktop applications, drag and drop file transfer, send webcam photos instantly, view replies and direct messages, very clean user interface.
  • twitterAIR — An AIR (Adobe Integrated Runtime) application built with Flex 3 that lets you view your friends and public timeline, post your status, and determine the auto-refresh interval.
  • Mugshot for Windows and Linux — show friends’ updates from your favorite services, including Twitter, on your desktop and the web
  • Spaz — An attractive, powerful Twitter client for Windows and OS X using the AIR platform. Direct messaging, deleting tweets, user management, and powerful skinning/theming via CSS.
  • Twitterbot — A simple bot written in C# (Mono/.NET) to reformat RSS feeds of news/sports/etc for Twitter
  • videotwit — Transcoding digital-to-digital conversion from one video format to another
  • Twerp — A simple command-line tool to post messages and download your friend’s timeline. Python 2.4 or 2.5..
  • PhotoTwitter. This application allows you to take a Snapshot using your Webcam and post the photo and your text on Twitter. Initially written for Mac but could also work on other platforms. Please let me know about problems on non-Mac platforms.
  • Twitter4Skype — Instructions on how to access your Twitter account in Skype. Developer here.
  • Tweeter — A Java desktop client for Twitter a-la Twitteroo but with proxy support. Lets you update your status and follow the public/ ‘with friends’ timelines, view images on the timeline, add/ remove friends, send direct messages, notifications on friends timeline update, minor GUI customization. ( Built with the jTwitter API from ThinkTank )
  • Twinja AIR — Twinja! A sleek black Twitter client built in Flash, running on AIR. Allows you to communicate with your Twitter friends directly from your desktop. Works on both Mac & PC.
  • TwitIt — A bookmarklet that is perfect for link/microblogging. You activate it while at a web page you want to share. It puts the current page title, a shortened URL (via TinyURL or tr.im) and selected text into the Twitter status box for final editing before submitting - you know - to get down to the 140 limit.
  • Snitter — lots of features with a great UI make this Twitter client stand out from the crowd. Built on AIR.
  • twhirl — A multi-account Twitter desktop client based on AIR and Flex. Compact UI, keyboard shortcuts, many features like auto-connect, auto-refreshing tweets, sending updates, replies, direct messages and more
  • twibble — A twitter desktop client with a clear UI. Supports multi accounts, iTunes like cover flow view and much more. Built on Adobe AIR for Mac and PC.
  • Posty - A microblogging application which allows updating twitter, jaiku, tumblr, friendfeed and identi.ca profiles with one click. Posty also includes: browsing of personal and public timelines, posting replies, browsing and posting of direct messages, support to favorites, search for past messages, automatic spellchecking, built-in url shortening. Posty is an Adobe Air application which runs on Windows, MacOsx and Linux.
  • Twitch - A cross platform Twitter client written using Adobe Air. Twitch focusses on having a clean and simple user interface.
  • IdentiTwitch - A cross platform Twitter client written using Adobe Air. IdentiTwitch combines your updates from Identi.ca and Twitter into a single timeline. Post to one or both services at the same time.
  • Twitter in your Profile - Plugin for Pidgin that lets you put your Twitter history in your profile. It updates automatically.
  • Toro for Twitter - Multi-platform Twitter client with a clean interface and an experimental Twitter client library that removed API limits and caching. Refreshes every 20 seconds.
  • Omnivide — Twitter Plugin - Omnivide is written in Java, so multi-platform. Only Mac OS X not supported due lack of Java 6. Twitter service provided via Plugin. Omnivide is a plugin powered program still in early stages of development.
  • Phweet - Phweet lets you talk to Twitter friends and create conference calls without sharing phone numbers or other ID’s. Phweet inserts a URL into your Twitter message so your profile becomes your callerID and your status update is the context for why you want to talk.
  • TweetDeck - TweetDeck is an Adobe AIR app which allows users to split their Twitter feed into topics and/or groups. Works on both Mac & PC. Still in beta.
  • P3:PeraPeraPrv - P3: PeraPeraPrv is Pure Java multi-platform Twitter client. P3 supports fully keyboard operation, filter view to tracking with @id and keyword, appearance customize, English/Japanese/Chinese interface and many features.
  • Twitter Thingy - A very simple Adobe air based Twitter client for windows, OS X and Linux. It has all the essential functions that get you using the best parts of Twitter as quickly as possible, without having to learn a colossal new bit of software. It also does groups and archiving.
  • TwitterSpy is a supplemental XMPP bot for twitter that does the stuff the twitter one used to do, and a few things it didn’: http://dustin.github.com/twitterspy/
  • tircd presents twitter as an irc channel. You can connect to tircd with any irc client and twitter as if you were on irc.
  • TickTagDo - A multi platform Task Management application that supports posting updates to Twitter. You can also automatically create tasks from your tweets. Just include ‘NTS:‘ (case insensitive) in your tweet and TickTagDo will use it as the base for a new task. So now you can add tasks from anywhere you can tweet. Direct messaging is also supported, easily lets you ask for progress on tasks via Twitter.
  • QTwittering - A very simple Qt4 based Twitter client for Linux, Mac OS X and Windows.
  • Simple Twitter Client: A simple, compact, open source desktop client written in Scala.
  • TweetFox - CloudBerry TweetFox is a Twitter plug-in for Firefox that helps you to post quotes from the websites you visit with a click of the button and attach a short Chilp.IT URL to the source page.
  • Twitter Gadget for Gmail - a Twitter client specially designed for Gmail using Opensocial technology.
  • Whisltr - A twitter + last.fm mashup in AIR.