Download by Aaron Newton | http://www.clientcide.com/js
A huge and on demand modular library containing more than 60 plugins, utilities and snippets maintained by the man behind the mootorial
Download by Greg Houston | http://www.mochaui.com/
MochaUI is a web applications user interface library built on the Mootools JavaScript framework that can be used in many ways : Web Applications, Web Desktops, Web Sites, Widgets, Standalone Windows and Modal Dialogs
Download by DM Solutions Group Inc | http://jxlib.org/
Jx is a javascript library for creating graphical user interaces based : combobox, dropdown select, trees ...
Download by Travis Beck | http://travisjbeck.com/blog/javascript/mootools-hidethismessage-plugin/
The basic premise is that you have a help message on one or more of your site’s pages which are incredibly useful the first few times the user visits that section. However, once the user understands how that page works, that once useful help message is now just in the way. So to solve this problem you might put a “Close this message” or “Hide this message” link in there so that your users can get it off their screen since it’s no longer needed