About the Eclipse Project
The Eclipse project is an Eclipse Foundation project, overseen by a Project Management Committee (PMC) and project leads. Development takes place in subprojects working on various GitHub repositories. The Eclipse Project Charter describes the organization of the project, roles and responsibilities of the participants, and the top-level development process for the project.
Equinox
The Equinox project provides an implementation of the OSGi core framework specification, a set of bundles that implement various optional OSGi services, and other infrastructure for running OSGi-based systems. It is the runtime basis for the Platform's plug-in runtime.
Platform
The Platform project defines the set of frameworks and common services that collectively make up "integration-ware" required to support the use of Eclipse as a component model, as a rich client platform (RCP), and as a comprehensive tool integration platform. These services and frameworks include a standard workbench user interface model and a portable native widget toolkit, a project model for managing resources, automatic resource delta management for incremental compilers and builders, language-independent debug infrastructure, and infrastructure for distributed multi-user versioned resource management.
Java Development Tools
The JDT project provides plug-ins that implement a Java IDE for power-users, that supports the development of any Java application, including Eclipse plug-ins. JDT adds the concept of Java projects and a Java perspective to the Eclipse platform, as well as a number of views, editors, wizards, builders, and code merging and refactoring tools. JDT allows Eclipse to be a development environment for itself. JDT's plug-ins themselves can also be further extended by other tool builders.
Plug-in Development Environment
The PDE project provides a number of views and editors that make is easier to build plug-ins for Eclipse. Using the PDE, you can create your plug-in manifest file (plugin.xml), specify your plug-in runtime and other required plug-ins, define extension points, including their specific markup, associate XML Schema files with the extension point markup so extensions can be validated, create extensions of other plug-in extension points, and so on. PDE makes integrating plug-ins easy.
Eclipse SDK
These four project comprise the Eclipse SDK a complete development environment for Eclipse-based tools, and for developing Eclipse itself.