Aptana Studio is an open source, integrated development environment (IDE) for building web applications. The newest version supports JavaScript, HTML, DOM and CSS with code-completion, outlining, JavaScript debugging, error and warning notifications and integrated documentation. Apart from being a great, colour coded coder – which is the main reason I’m using it at the moment – it can show you what browsers supports the code you’re using and is probably one of the better new HTML5 editors.
Best of all, Aptana Studio 3 is absolutely free!
Additional plugins allow Aptana Studio to support Ruby on Rails, PHP, Python, Perl, Adobe AIR, Apple iPhone and Nokia Web Runtime.
Aptana Studio 3 is available on Mac OS X, Windows (x86 – x64 Compatible) and Linux operating systems.