In the left hand textarea, type some tiny Forth (\d+|+|-|*|/|swap|dup|pop|rotate) and watch the fun explode onto your screen when the box loses focus (or you click on update).
Stack can be forced with (*( stuff ))
Comments ( look like this )
Errors are reported in the javascript: console

Tested on Netscape 4.51.
(c) 1999 Tim Baverstock