Commercial plug-ins are built on one or more base plug-ins that are shipped as part of Eclipse. They are broken down into several groups, further separated into UI and Core, as follows. UI plug-ins contain aspects of a user interface or rely on other plug-ins that do, while you can use Core plug-ins in a headless environment (an environment without a user interface).
Core A general low-level group of non-UI plug-ins comprising basic services such as extension processing (see Chapter 9, Resource Change Tracking, on page 375), resource tracking (see Chapter 17, Creating New Extension Points, on page 595), and so on.
SWT The Standard Widget Toolkit, a general library of UI widgets tightly integrated with the underlying operating system (OS), but with an OS-independent API (see Chapter 4, The Standard Widget Toolkit, on page 127).
JFace A general library of additional UI functionality built on top of SWT (see Chapter 5, JFace Viewers, on page 185).
Workbench core Plug-ins providing non-UI behavior specific to the Eclipse IDE itself, such as projects, project natures, and builders (see Chapter 14, Builders, Markers, and Natures, on page 497).
Workbench UI Plug-ins providing UI behavior specific to the Eclipse IDE itself, such as editors, views, perspectives, actions, and preferences (see Chapters 6, 7, 8, 10, and 12).
Team A group of plug-ins providing services for integrating different types of source code control management systems (e.g., CVS) into the Eclipse IDE.
Help Plug-ins that provide documentation for the Eclipse IDE as part of the Eclipse IDE (see Chapter 15, Implementing Help, on page 539).
JDT core Non-UI-based Java Development Tooling (JDT) plug-ins for the Eclipse IDE.
JDT UI JDT UI plug-ins for the Eclipse IDE.