jQuery & Javascript
I’ve worked with jQuery and standard JavaScript on pretty much every site I’ve had to work on. You’d struggle to create a dynamic / animated website without the use of JavaScript in some form or another.
jQuery dose however have its downsides, its made people lazy, writing jQuery is easy, pretty much anybody can do it with limited knowledge of HTML selectors, now there is nothing wrong with this in a sense, but using a library because it makes it ‘easy’ when the same can be achieved with plain JavaScript makes for lazy coding!