Aaron Newton has posted a Mootools Primer / Tutorial that includes “a how-to tutorial on the Mootools library. Most of the code examples will allow you execute them by clicking on the “execute this code” link above the example. Clicking this will echo out the code and the result in the Firebug debugging plugin for Firefox. You’ll need that plugin installed to see any results of most of the code examples.”
Currently the tabbed widget shows documentation for the core Moo.js, extensions of JavaScript objects and helpers, Addon libraries, and plugins.