STATUS ALERT: The Tweetmeme.com service is not responding Thursday morning. The green Twitter counter is replaced by a blue bar during the outage.
Tweetmeme.com is the entity behind the little green web button that counts how many times users share links on Twitter. The goal of the website is to get more people to share content on Twitter’
Tweetmeme claims over 750 million daily retweet button impressions. Recently Tweetmeme announced that Twitter is launching its own Tweet Button and that Tweetmeme will be partnering with Twitter to continue to “grow the overall Twitter ecosystem.”
Wikipedia: List of Twitter services and applications