It’s the Christmas tree that’s controlled by Twitter. The Tweettree has a small embedded server and the fiber optic tree will change it’s color to the one that you tweet! Now you probably want some proof that when you tweet it’s actually changing- no problem- you can follow the live streaming video at UStream. To make the tree change colors just tweet @tweet_tree with the color or colors- it understands basic colors and hexadecimal color codes as well as color combinations to cycle through (full instructions and build information available here).