What is "mootools"

Mootools focuses on making the Javascript API more stable and coherent, it is less focused on offering an interface that "changes the way you write Javascript" and more in making language as a much less frustrating whole.

Code example:

window.addEvent('domready', function(){
    document.getElements('a').addEvent('click', function(event){
        event.stop();
        console.log('Olá! Este link veio de um link com o url: ' + this.get('href'));
    });
});

Official links:

mootools.net - official page
github.com/mootools - code reset in development
#mootools - IRC channel on freenode for support and discussions with the Mootools team plug-ins - official plug-ins available

About Mootools

jQuery vs Mootools - Excellent text on Mootools applications and their particularities.