I know this is a crap answer to this question, but for me what is "cool" is what can easily do things that I think are awesome. For me, that's Angular.js.

http://angularjs.org/ Angular UI is amazing http://angular-ui.github.com/ And Angular for Bootstrap is also amazing http://angular-ui.github.com/bootstrap/

I'm not a great programmer, so that's what excites me. It's flexible enough that as you get better as a programmer, you can plug that right in.

And that's what I think is cool.