Listed below is a huge collection of Twitter tools, along with information and links to articles and reviews on each. If you have any to add, leave a comment as I will be updating this post as I go on. (Shit, AJAX is the bomb.) This should become your number one Twitter resource starting now mmmmkay.

Web Applications                  
1. Twitt(url)y – A service for tracking popular URls that are being shared across the Twitter network. Useful for identifying hot trends and topics within social networks.
   1. Twitturly: Tracking Popular URLs On Twitter [The Startup Review]
   2. Twitturly Cracks The TwitterMeme Nut
   3. CrunchBase – twitt(url)y company profile
2. FollowBack – Gives you a color-coded view of people who are following you, and if you should follow them back.
3. Group Tweet – Anyone who wants to broadcast and share private tweets to a specific group of people can do so for free with Group Tweet. Think of it as Yammer but within Twitter.
   1. Privacy Disaster At Twitter: Direct Messages Exposed (Update: GroupTweet Is Likely Culprit)
   2. GroupTweet to blame for Twitter security ‘compromise’
   3. GroupTweet Enhances Twitter
   4. CrunchBase – GroupTweet Company Profile
4. Tweetmeme – Tracks hot topics on Twitter bases on the links people are sharing. 
   1. CrunchBase – Tweetmeme Company Profile
   2. TweetMeme Returns Following Months-Long Forced Outage
   3. Meet Tweetmeme, The Sweeter Way to Track Twitter
5. TwitLinks – Aggregates links from the worlds top tech Twitter users.
   1. TwitLinks: The Techmeme Killer of Twitter? – ReadWrtieWeb
   2. TwitLinks Company Profile – CrunchBase
   3. TwitLinks: Not Useful, Not A TechMeme Killer – TechCrunch
6. Favrd – Offers channels of the most favorited tweets on Twitter with options to search and identify topics by keyword.
   1. FAVRD: Entertainment for the Twitter Attention Span
   2. Fail Whale for the Favrd
7. TweetLater – Schedule tweets for a particular time or day and also allows you to auto-follow and one who follows your account. They even offer a auto-welcome feature that sends a welcome message to your followers.
   1. TweetLater.com – Tweet into the Future
8. Twist – An aggregation like service that looks at trend comparisons and volume between keywords and tags.
9. Twubble – Introduces and recommends new people you may want to follow based off your friend graph.
10. WhoShouldIFollow – Pretty much like Twubble.
11. Twellow – A very useful tool for finding people who matter in your business, industry, or niche.
12. TwitDir – A very effective people search tool for Twitter.
    1. 1 million Twitter users according to Twitdir
    2. A showdown of Twitter user directories – TwitDir vs. Twitterholic
    3. Tracking Your Twitter Growth With Twitterholic, TwitDir, Tweeterboard & Others
13. Twerp Scan – Keeps an eye on the friend / follower ratio of your friends and their friends.
14. Tweet Pro – A paid service for creating a solid niche based network. Great for use in business/branding.
15. Tweet Scan – A search engine for Twitter with advanced topic and trend/keyword tracking features.
16. twInfluence – Measure Twitter influencers based on reach, velocity, social capital, and more. 
17. TwitterGrader – Measures the relative power and authority of a Twitter user by calculating the number of followers, the power of the network of followers, the pace of updates and the completeness of a user’s profile.
18. TwittAd – Micro ad network that connects advertisers to Twitter users to create opportunities for paid product placement and website promotion directly on a Twitter user’s profile.
19. Twitterise – Advertise on Twitter and track the success of branded communications with your customers.
20. WhatsYourTweetWorth – Analyzes your account and network to recommend what your tweets could be worth on Twittad.
21. Twitterific – Lets you read and publish tweets from the desktop, iPhone and iPod Touch.
22. TwitterWhere – Provides the ability to update Twitter with your current location.
23. TwitterFeed - connects your blog to Twitter and automatically feeds posts into the timeline with each new update.
24. Tweetbeep – Allows you to monitor conversations that mention you, your brand, related or competitive products, as well as links to your website or blog, even if they use a shortened URL, such as tinyurl.com.
25. Ping.fm – A central distribution service for sending updates to multiple social networks, including Twitter, with one click. 
26. Hellotxt – Provides the ability to instantly update status as well as view the status of your contacts across multiple networks (Facebook, LinkedIn, hi5, Plaxo, Pownce, Plurk, FriendFeed, Identi.ca, BrightKites, etc.) – all from one dashboard.
27. Matt - (Multiple Account Twitter Tweeting) provides a platform for broadcasting one update to multiple accounts.
28. FeedTweeter – Connects social services that offer RSS feeds to you Twitter account.
29. TweetWheel – Visually presents your social graph, who’s following you and who you are in turn following.
30. Twiffied – Shows the headlines of the Websites your Twitter friends have listed in their profiles to see what they’re linking to or blogging about.
31. BrightKite – A location-based social network that connects directly to Twitter.
32. TwitterLocal – The ideal service for quickly finding active voices within a specific city, state, postal code as well as the vicinity, ranging from 1 mile to 20.
33. SnapTweet -  Links your flickr account to share updates seamlessly to Twitter.
34. DoesFollow – Lets you know if one person is following another. That’s it.
35. TwitPic – Provides a bridge from your camera phone to Twitter. Pictures can either post to the Twitter public timeline from phone via email or through the site.
36. Tweet2Tweet – Provides you with the ability to view a history @replies between two Twitter users.
37. Qwitter – Will send an email to you when someone unfollows you and will link the action to the most recent tweet that you posted.
38. FollowCost – Estimates the potential attention (or annoyance) cost of following a particular individual or account.
39. TweetPad – Provides a visual representation of Twitter feeds and statistics with dynamic typography.
40. Twitzu – An event invitation management service for Twitter. You can create an event, broadcast it to followings and manage RSVPs.
41. xefer – Reviews your Twitter account and presents a rich visual analysis of your tweet volume, concentration as well as their resonance (measured by replies) by day, time, week and hour.
42. LiveTwitting – A streamlined solution for livetweeting (covering) conferences.
43. TwitterKeys – Enhances Twitter conversations by replacing words with UTF8 compatible images.
44. Twalala – Adds a mute button to Twitter allowing you to focus your stream as necessary without completely unfollowing someone.

Twitter Clients

45. Twhirl – A social desktop dashboard that centrally manages activity, messaging, and updating for Twitter, FriendFeed, Identi.ca, and Seesmic.
46. TweetDeck - An Adobe Air desktop app that enables uers to split their main Twitter feed into topic or group specific columns.
47. Google Twitter Gadget - Twitter gadget from Google thats pretty much an add-on for Google Desktop.
48. Twitteroo - Has some nice features including URL shortening, sound notification and many other features which help you speed up your tweeting.
49. Spaz – An extremely customizable desktop Twitter client which is available on Windows, Mac and Linux.
50. Witty – A good looking Twitter client which works with Windows Vista and XP.
51. TwitBin - Available to Mac, Windows and Linux owners, TwitBin is a plugin for Firefox 2.0+.
52. Tweetr - Available on Mac and Windows, Tweetr is a great looking Twitter Client. There are alternatives with more features however it’s still worth checking out.
53. Snitter – One of the best looking desktop Twitter clients available.
54. Twitter Opera Widget – A Twitter widget for Opera with basic features.
55. Twibble - The Twibble desktop client is available on Mac and Windows. It allows you to add multiple profiles and even lets you see where you’re Twitter friends are via google Maps.
56. Pwytter - Available on Windows, Mac and Linux, Pwytter has been translated into a whopping 14 languages.

Mobile Twitter Tools

57. Twitterfon – A fast, simple Twitter client for the iPhone and iPod Touch. It is focused on 80% of your tasks in Twitter such as viewing friends/replies/messages in the timeline and also sending/replying tweets.
58. Twinkle – A location-aware network for the iPhone and iPod Touch that helps you discover, connect, and send messages to the public timeline and also to people nearby.
59. Twittlelator – A Twitter client for the iPhone. You can manage multiple user accounts, update your accounts, share pictures, a map of your current location, connect with other Tweeps, read tweets from your contacts, and direct message (DM), and reply all from one app.
60. Twitterberry – A full-featured Twitter client to read and post updates from BlackBerry phones.