Twitter - Social networking and microblogging service utilising instant messaging, SMS or a web interface.

Commuter Feed

Commuter Feed - Get traffic and transit updates from Twitter posts.

Featured Users

Featured Users - An ad network of Twitter applications where Twitter users advertise their profile to gain followers.

Follow Cost

Follow Cost - Follow cost measures how frequently people tweet.

Friend Or Follow

Friend Or Follow - Twitter followers management application that shows the user who they are following that is not following them back and vice versa.

FutureTweets

FutureTweets - A free service that lets users schedule Twitter messages at a specific time in the future or send a recurring Tweet at daily, weekly, monthly or yearly intervals.

Hashtags.org

Hashtags.org - Tracks the frequency that a hashtag is used on Twitter and provides details about the hashtag.

Just Tweet It

Just Tweet It - Directory of users classified by interest and occupation. Also includes tools, services and latest news.