Here's a demonstration of AGATE operation. You need to have Java enabled, and despite fiddling around with it, it doesn't seem to want to run on anything lower than Java 1.4, sorry! (If you know why this happens, please email me; I'd like to fix the problem.)
There are four grammars that you can select from the "File" menu:
You can also tweak the animation speed (or turn off animation completely) from the menu. Not surprisingly, animation works well on a fast machine, probably not so well on, say, a Commodore 64.