Twitterslurp - a drop.io API app that creates a keyword Twitter stream, with a list of users and stats for your website, see an example at the Personal Democracy Forum created by the Bivings group.
[ADDED 4/07/09 - Please ignore the Drop.io reference as Twitterslurp by the Bivings Group is based on this googlecode]
Tweetboard - showcase a Twitter stream in your blog. The owner and visitors to your site populate this stream by tweeting in the text box. All replies are threaded. View a history of all tweets or the lastest ones.
Rather than embed this app in your blog, it acts as a tab on the side of the browser window, which you click and a window expands. If this tab is red it means there are new tweets (from the owner and visitors) since your last visit; if it’s green means otherwise.
When someone tweets in the text box provided, the tweet appears at Twitter with a special link called “posted.at” at the end of the tweet. This is a unique link that points back to the site, and opens up that thread…this brings traffic back to your site where the visitors can participate in the thread discussion.
When browsing a sites Tweetboard you can click the permalink of a tweet and it launches a text box where you can copy the permalink of that tweet. You could paste this link into a blog post or a tweet, whatever…I guess this pop-up box spoonfeeds you rather than having to right-click, then copy shortcut.
Further to this, each reply in a tweetboard thread also has a special link called “inreply.to”. When someone clicks the permalink of a reply, a box pops up with the link to that spot in the thread on the tweetboard of that site. If you are reading a reply in the thread and click reply, and enter a tweet, that tweet will appear in twitter with a link back to that exact spot in the thread.
Tweexchange - see if a user name is available