MooTools is a compact, modular, Object-Oriented JavaScript framework designed for the intermediate to advanced JavaScript developer. It allows you to write powerful, flexible, and cross-browser code with its elegant, well documented, and coherent API.

MooTools code respects strict standards and doesn't throw any warnings. It's extensively documented and has meaningful variable names: a joy to browse and a snap to understand.
Open Source License

MooTools is released under the Open Source MIT license, which gives you the possibility to use it and modify it in every circumstance.
Browser Compatibility

MooTools is compatible and fully tested with Safari, Internet Explorer 6+, Firefox, Opera, and Chrome.


BOOK LIST
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- MooTools 1.2 Beginner's Guide

- Pro JavaScript with MooTools

- MooTools Essentials: The Official MooTools Reference for javascript and Ajax Development