Looks great and looks like it will run as an Eclipse plug-in! What more could you ask for. Not sure how it compares to the latest Eclipse 3.2 (Callisto) Web tools platform – which I use and love.
“Aptana is a robust, JavaScript-focused IDE for building dynamic web applications. Highlights include the following features:
- Code Assist on JavaScript, HTML, and CSS languages, including your own JavaScript functions
- Outliner that gives a snapshot view of your JavaScript, HTML, and CSS code structure
- Error and warning notification for your code
- Support for Aptana UI customization and extensions
- Cross-platform support
- Free and open source. (Source available soon)”
James McParlane's Blog 
Hi,
I just looked thought the screencast for aptana and tried it withouth elcipse.
I am very impressed at the Code Assist on JavaScript and error notifications – which I am always in need.
Well done to aptana for a great IDE!