excla.im - Since Twitter has dropped it’s IM feature (which was broken), we have a 3rd party replacement…also see TwitterIM, and whatever happened to IMified Twitter.
Twitterkeys - add symbols to your tweets via a bookmarklet
eg. I ♥ you, you make me want to ♫
Dwigger - memedigging for Twitter. Enter a tweet URL or write a tweet within Dwigger and wait for the comments and voting [via m]
Social Tops - how many popular Twitter sites can you get, also see TweetMeme, TwitLinks, Twit(url)y and others
Tweader - what I like about Jaiku is that when you reply to a post, your reply becomes a post itself in the stream, but at the same time it’s also a threaded comment under the post you are replying to.
Twitter can’t do this as when you reply by SMS, how does it know which tweet you are replying to, instead it default threads it under the last tweet, as well as becoming a tweet of its own. As a result of this you won’t see a comments stream under a tweet.
BUT, if many people reply to a tweet before that person makes a new tweet, this can be shown as a threaded conversation using Quotably. Twitter could easily do this, it’s just bunching up the replies between your last tweet and your next tweet. But we still have the problem that if you make a new tweet, a person can no longer direct a reply to your previous tweet, instead it will be threaded under the new tweet, which means the conversation sometimes doesn’t make sense. Tweader like Quotably does not achieve anything new…also see TweetDeck.
Sometimes people use #hashtags (and track them at Twemes), but this is more tweets about a topic, event, subject, etc…you can even limit this to a bunch of people using Twitter Teams, and Twitter Soap comes close to threaded tweets, but still it’s not an easy and regular way to have threaded conversations.
BONUS
Connect The Tweets