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Eclipse is an open-source, platform-independent software framework, written primarily in Java, for delivering what the project calls "rich-client applications", as opposed to "thin client" browser-based applications. So far this framework has typically been used to develop Integrated Development Environments (IDEs), such as the Java IDE called Java Development Toolkit (JDT) and compiler (ECJ) that comes as part of Eclipse (and which are also used to develop Eclipse itself). However, it can be used for other types of client application as well.
For more details pls visit:: http://www.eclipse.org/