Library clips

Hootsuite - manage multiple Twitter profiles, add multiple editors to a profile without password hassle, pre-schedule tweets, measure your success, and a tweet bookmarklet.

Nearby Tweets - view a tweet stream based on the location field in Twitter bios. You can also filter it by keyword. See similar here.

Twimailer - you know when you get an email notification of a new person who is following you, well the email doesn’t tell you anything about that person. In comes TwiMailer, once you join up it gives you a unique email which you have to enter in your Twitter profile settings. Now when you get an email of a new follower, it displays their bio, avatar, their following and follower stats, and a stream of their latest tweets, and a link to follow them back…all that’s missing is a “block” or “remove” link. I wonder if this could also hook up with Qwitter.

Retweetability Index - retweets + tweets per day / Followers. Search by topic or by user. Also see RetweetRadar and others.

Top Twitter Friends - a cool social graph tools where you can: see your conversations, see your towns social network, see people who talk about you.

BONUS
The 140 character webapp challenge!

Twitter search results on Google - a greasemonkey script on FireFox that displays latest results from Twitter on Google search results

Search Cloudlet - A FireFox extension for Google and Twitter, that generates a keyword cloud with the search results, for frequent words that appear with the search query. Besides a tagcloud it will also offer a site search cloud on Google, and on Twitter it will list a cloud for authors, replies and hashtags.
Also noticed that there is a tag cloud on a Twitter profile page, as well as a reply cloud.

wwwitter - When I tweet the page I’m on I usually use TwitSnip, TwitThis, or Bit.ly, well now wwwitter is a new contender. Like the others it works as a bookmarklet, and like TwitThis you can also copy some code into your site, perhaps as a blog post footer button. But it also does something similar to bit.ly in that it will display existing tweets about that page. Also see Backtweets , which I posted about yesterday.

filttr - an alternative interface for Twitter that is focused on filtering. It has inline replies, and you can attach files. It has sliders for people you follow, indicating how often you want to see their tweets. There is a blacklist and whitelist for words you want to filter out/in…you can even filter out “sources” eg. Twitterfeed, Friendfeed, etc… You can also make groups streams, keyword streams, or a combination of both. You can use it on the web interface, mobile web, app, and IM.
The only thing I see missing is to be able to filter a stream by limiting to tweets that contain links.
I have listed a few things over on Uservoice.

Tweetpkr - a bookmarklet that will open your Twitter stream as a sidebar in the current window you have open

BONUS
6 weird and wonderful things people have built with twitter