Twitter's JavaScript API designed to allow easy integration of Twitter features with websites. This API has been scheduled for deprecation in March 2013.
Twitter @Anywhere is described as an easy-to-deploy solution for integrating the Twitter communication platform with websites. The @Anywhere API provides methods for websites to add Follow Buttons, Hovercards, linkified Twitter usernames, and TweetBoxes. @Anywhere is scheduled for deprecation in March 2013.