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Twitter is a free social messaging utility for staying connected in real-time.
Display Twitter updates on your web page.
Here’s a neat way to let visitors to your blog or profile page on the web know what you’re up to at the moment: Display your latest updates there with a customized widget (aka, “badge”).
Flash and HTML widgets [...]

If you are using #followfriday to endorse your friends …
TopFollowFriday will let you see who endorses you, and who endorses whom!

If you are using #followfriday to endorse your friends …
… TopFollowFriday.com will let you see who endorses you
TopFollowFriday is a website that allows you to explore who is recommending who using the #followfriday hash tag.
Go now to: TopFollowFriday

TwitSeeker is an alternate search engine for finding twitter.com users - “twits” - and browsing the results all in one combined control panel.
It works by using the twitter.com API, and finds twits not by what’s posted in their bios but rather based on what they’ve been tweeting about lately.
It uses a custom tag cloud generator written [...]

Find the people on Twitter that share what you share!
TwittGroups.com brings people together from Twitter with common interests.
Find an existing group with people that you can follow.
Join groups that interest you.
Create new groups for your organizations, business, schools and clubs.
Go now to: Twitter Groups

Your Personal Networking Assistant for Twitter, helping you identify relevant followers, recommending you to other users, and regularly computing your twitter usage statistics.
Mr. Tweet is your personal networking agent who helps you expand your network easily. To do that, he helps you regularly:
 

Get relevant followers by recommending you to them
Discover great people relevant to your [...]

According to the official Twitter FAQ, “Twitter is a community of friends and strangers from around the world sending updates about moments in their lives. Friends near or far can use Twitter to remain somewhat close while far away. Curious people can make friends. Bloggers can use it as a mini-blogging tool. Developers can use [...]

Your Personal Networking Assistant for Twitter, helping you identify relevant followers, recommending you to other users, and regularly computing your twitter usage statistics.
Go now to: Mr. Tweet

Enter a few words or phrases and see how often they appear on Twitter.
Go now to: TweetVolume

Getting to know Twitter - What is it?
Twitter is a service for friends, family, and co–workers to communicate and stay connected through the exchange of quick, frequent messages.  People write short updates, often called “tweets”  of 140 characters or fewer.  These messages are posted to your profile or your blog, sent to your followers, [...]