In Eclipse, everything is a plug-in. Even the OSGi framework and the Equinox functionality show up as plug-ins. All plug-ins interact via the extension registry and public API classes. These facilities are available to all plug-ins. There are no secret back doors or exclusive interfaces—if it can be done in the Eclipse IDE, you can do it in your application.
SWT, JFace, and the UI Workbench plug-ins combine to form a powerful UI framework that you can use to build portable, highly scalable, and customizable UIs that have the look and feel of the platform on which you are running.
In short, Eclipse is an ideal technology for building modular RCPs based on OSGi.