It’s been out there for some months already, but I just discovered it through Yahoo! User Interface Blog: Aptana is a robust, JavaScript-focused IDE for building dynamic – AJAX - web applications.

It is available as a standalone app for Windows, Linux and Mac; and of course as an Eclipse plug-in too (which is in my opinion the solution most of people will choose).

A screencast – embedded in the Yahoo! blog post linked above – is showing Aptana’s most significant features, and its YUI support. Very nice.