Here’s a video where Chris demonstrates Twickie and shares how and why he created it.
Here are a few others of note:
was a decent service that tried to do this but it’s no longer with us. It also wasn’t very accurate. It displayed many replies but sometimes they weren’t really in response to that tweet.
Tweader uses the tweet ID or the URL to your tweet to aggregate any responses to that particular tweet. The results are varied and it’s not as easy to copy and paste the results like on Twickie.
Twonvo is another service similar to Tweader that attempts to thread conversations based on the tweet ID. Enter the ID and it pulls related tweets.