Zest 0.3 is now available (
https://github.com/mozilla/zest/tree/master/dist) and has been included in ZAP 2.2.0 (
http://code.google.com/p/zaproxy/downloads/list).
Its got loads of changes from the last version - at some point I'll try and document everything.
But right now the best way to get started with Zest is to download ZAP and play with it.
There is a basic help page included, which is also online:
http://code.google.com/p/zaproxy/wiki/HelpAddonsZestZestI will try to improve the documentation and record a video as soon as I can.
In the meantime please feel free to ask any questions on this list.
And raise issues for any problems you find, or enhancement requests for features you would like to see.
Thanks to Alessandro for his contributions to Zest as part of the Google Summer of Code 2013.
Cheers,
Simon