via) It's the Tweeter 140, via pen and marker company Artline. From the press release:
"A series of accelerometers and a small sensor mounted in the barrel track the pen's movements and translate that into characters. A specially designed fourth generation microchip allows the pen access to your Twitter account, updating it instantly. The ability to physically express something in writing then posting it makes the tweeting experience much more tactile and therefore more enjoyable. It's something people have really been missing."
Mine's on order.