jQuery doesn't focus on things outside of the DOM. This is one of the reasons it is so easy to learn, but it also limits the ways it can help you write JavaScript. It's just not trying to be anything other than a solid programming system for the DOM. It doesn't address inheritance nor does it address the basic utilities of all the native types in the JavaScript language, but it doesn't need to. [...]

This is where MooTools is vastly different. Rather than focusing exclusively on the DOM (though, as I'll get into in a bit, it offers all the functionality that jQuery does but accomplishes this in a very different manner), MooTools takes into its scope the entire language. If jQuery makes the DOM your playground, MooTools aims to make JavaScript your playground, and this is one of the reasons why it's harder to learn.