Eclipse Plugins
"Out of the box - or off the web - the basic [Eclipse] platform is an integrated development environment (IDE) for anything (and nothing in particular).
It's the plug-ins that determine the ultimate functionality of the platform. That's why the Eclipse SDK ships with additional plug-ins to enhance the functionality of the SDK."
http://help.eclipse.org/indigo/index.jsp?topic=%2Forg.eclipse.platform.doc.isv%2Freference%2Fmisc%2Ffeature_manifest.html