I still love MooTools. It should be where jQuery is with regard to mindshare. A lot of people didn't like the fact that it extended globals, but whatever it works well and you can easily build very complex systems with the class structure. I made this object pool using MooTools as an example on how to reuse instantiated objects http://jsfiddle.net/XkTPJ/
I told myself recently that it's actually mootools who won. Most cool stuff mootools does on natives is now standard since ES5/6 - either in the exact same form or something similar. On the contrary, jQuery is consistently losing ground in favor of "vanilla js" (that is, babel, really).
Even if most frontend devs didn't use mootools, the way they code nowadays is very similar to what mootools was pushing for. This biggest difference I see being that we still don't have animations and requests as objects that can be reused (but css animations are probably more performant, and fetch + async/await is cooler).
