Closure Library is a powerful, low level JavaScript library designed for building complex and scalable web applications. It is used by many major Google web applications, such as Gmail and Google Docs.

You can read more about Closure Library at http://code.google.com/closure/library

The Closure Library docs: http://closure-library.googlecode.com/svn/trunk/closure/goog/docs/index.html

Browse the source: http://code.google.com/p/closure-library/source/browse/#svn/trunk

The Closure Library discussion list: https://groups.google.com/group/closure-library-discuss