Shapiro says that he was tired of visiting sites like CNN and not being able to leave a comment without logging in, so he built a way to get around that using the browser and his Twitter identity. The idea took shape as AddATweet, giving us all an instantaneous way to leave a comment wherever we'd like.
AddATweet is exactly as it sounds: it's a service that lets you add a tweet/comment to any webpage. The Firefox plugin supports comments by creating a browser-based sidebar where you can view, add, filter, and tweet comments. To use AddATweet, just click the button in your browser's toolbar (in the upper right hand corner) to open the comment sidebar where you can view existing page comments and add your own once you connect your Twitter account to AddATweet using Sign in With Twitter.
It's a simple idea that's pretty nifty in practice. We really like that you can view all comments (everyone), filter for just your network (following), or see comments ranked by commenters' follower count (authority). All comments are threaded, and you can not only reply directly to comments in the sidebar in familiar Twitter-style, but you can also retweet, reply to a Twitterer, or mark comments as spam.
Of course, AddATweet is more of a commenting platform than a way to add a tweet to a web page, but it uses your Twitter identity in an intelligent way to strip comments from publisher-owned entities and turn them into user-controlled spaces. It's still a very new service, so we expect to see AddATweet evolve in feature set, but as is, we find it be a clever way to tap into our Twitter identities to create conversations with our friend networks.
For a quick overview, watch this demo of AddATweet: