Instead of trying to rework some of the UI elements of the Chrome browser to make room for sharing and/or social elements, Cortex simply adds a sharing overlay to any site you’re on when you click and hold down your mouse button. Using this mechanism, you can share to Facebook, Twitter, Tumblr, or Instapaper (assuming you set up each of those). It’s simple and brilliant.
http://techcrunch.com/2010/12/15/cortex-chrome/
