This help topic gives an overview of how Aptana Studio and Eclipse IDE are related.
Introduction
The Eclipse Integrated Development Environment (IDE) is open-source software for application developers. While the Eclipse IDE itself is targeted at Java developers, many IDEs are based on Eclipse and are targeted at other programming languages. For example, Aptana Studio is designed for web developers and provides robust support for HTML, CSS, and JavaScript, and Aptana Rails focuses on Ruby on Rails development.
Both Aptana Studio and Aptana Rails are available as standalone applications or as "plug-ins" to Eclipse. To learn more about how plug-ins work with Eclipse and Eclipse-based development environments, see About plug-ins.