JQuery UI

jQuery UI is a collection of GUI widgets, animated visual effects, and themes implemented with jQuery (a JavaScript library), Cascading Style Sheets, and HTML. According to JavaScript analytics service, Libscore, jQuery UI was used on over 197,000 of the top one million websites, once making it the second most popular JavaScript library. Notable users were Pinterest, PayPal, IMDb, The Huffington Post, and Netflix.
Both jQuery and jQuery UI are free and open-source software distributed by the jQuery Foundation under the MIT License; jQuery UI was first published in September 2007.
Features.
As of the 1.11.4 release, interactions such as draggable/droppable and sortable are supported. jQueryUI comes with fully themeable widgets using a consolidated, coordinated theme mechanism, such as Autocomplete, Datepicker, ProgressBar, Sliders, and more.
Effects include color animations, class toggling. 
Example.
// Make the element with id "draggable" draggable
$(function () {
 $("#draggable").draggable();
<div id="draggable">
 <p>Drag me around</p>
</div>
This makes the div with the ID "draggable" draggable by the user's mouse.