4aos - a small OS on the UNO

Maybe someone is interested in testing and editing small apps that are executed via an interpreter on the arduino UNO itself. A short description of my project (that is based on a TFT-touch-shield with a sd-card) can be found here:
http://playground.arduino.cc//Main/4aos

Well its all quite basic and a lot of compromises had to be made (32 kB of compiled code and 2 kB RAM isn't really much), but in the end its nearly a stand-alone OS (obviously no interrupt-control, no multitasking...).
Any ideas to improve this project are welcome. Here's a short demonstration:

The source code is too long for this post, you will found the link to 'gzipped' folder in the 'playground'-article.

Finally I found time to add the code to the description of the project:
http://playground.arduino.cc//Main/4aos#scode

And here's the link to the touch display I'm using (my latest version has a different pin layout from the one in the link - as I mentioned in the code):
http://imall.iteadstudio.com/im120417012.html

Because of the USB-connector I recommend using a simple screw shield:

What is the modified code for your new shield? I also have a 2.8 itead tft touchscreen but it doesn't display anything when I upload your OS