The Closure Tools project is an effort by Google engineers to open source the tools used in many of Google's sites and web applications for use by the wider Web development community.
The Closure tools help developers to build rich web applications with web development tools that are both powerful and efficient. The Closure tools include:
The Closure Library is server-agnostic, and is intended for use with the Closure Compiler.
Closure Templates simplify the task of dynamically generating HTML. They have a simple syntax that is natural for programmers. In contrast to traditional templating systems, in which you use one big template per page, you can think of Closure Templates as small components that you compose to form your user interface.
An enhanced stylesheet language
Closure Stylesheets is a system that supports a number Google extensions to the standard CSS language. With these extensions, you can define and use variables, functions, conditionals, and mixins in your stylesheet, making your stylesheets more readable and maintainable. An included tool can compile the stylesheet down into standard CSS and supports minification, linting, directionality (right-to-left flipping), and class renaming.