Has anybody tried Jaxer? From the people that make Aptana.
(http://www.aptana.com/jaxer)
Basically it allows you to use JavaScript on the server and on the client. So, for example you only need to write your form validation routines once.
It's very cool, particularly if you like your web 2.0 ajax stuff... I think it looks like it could get messy if you were to use it for large websites, or at least confusing with various levels of JavaScript (ie. server side, client side both...).
