The Eclipse Project is an open source software development project dedicated to providing a robust, full-featured, commercial-quality, industry platform for the development of highly integrated tools. The mission of the Eclipse Project is to adapt and evolve the eclipse technology to meet the needs of the eclipse tool building community and its users, so that the vision of eclipse as an industry platform is realized.
Eclipse is a kind of universal tool platform - an open extensible IDE for anything and yet nothing in particular. The real value comes from tool plug-ins that "teach" Eclipse how to work with things - java files, Web content, graphics, video - almost anything one can imagine. Eclipse allows tool builders to independently develop tools that integrate with other people's tools so seamlessly you can't tell where one tool ends and another starts.
Note: The download file is an installer that let's you chose what packages to install.