Zoomerang.js is a drop-in library that allows your users to zoom in on (almost) any element on your existing page. No setup, arbitrary styling. And it works even if you resize or scroll your page.    

JqTree is a tree widget for jQuery.   JqTree - Features: Create a tree from JSON data Drag and drop Works on ie7+, firefox 3.6+, chrome and safari Written in Coffeescript    

Gridly is a jQuery plugin to enable dragging and dropping as well as resizing on a grid.    

CamanJS is canvas manipulation in Javascript. It's a combination of a simple-to-use interface with advanced and efficient image/canvas editing techniques.   It is very easy to extend with new filters and plugins, and it comes with a wide array of image editing functionality, which continues to grow. It's completely library independent and works both in NodeJS and the browser.    

FileAPI is a set of javascript tools for working with files. Multiupload, drag and drop and chunked file upload. Images: crop, resize and auto orientation by EXIF.     

Mosaiqy is a jQuery plugin to organize and show image thumbnails and zoom, easy to integrate also with Flickr, Instagram, Panoramio and other.  Thumbnails are arranged in a grid and each row and column could be randomically moved, sliding in every direction and showing other thumbnails available. Image data is described as a regular JSON object.  And all expensive animations are taken over by your GPU on recent browsers using CSS3 transitions, minimizing the CPU overhead.     

Picbox is a lightweight javascript image viewer based on the excellent Slimbox by Christophe Beyls, and available using either the Mootools or jQuery frameworks. It features automatic resizing and zooming of large images, allowing them to fit in the browser or be viewed at full size.    

Tipsy is a jQuery plugin for creating a Facebook-like tooltips effect based on an anchor tag's title attribute.    

WikiUp is a jQuery plugin which gets Wikipedia descriptions in tooltips.    

FullCalendar is a jQuery plugin that provides a full-sized, drag & drop calendar. It uses AJAX to fetch events on-the-fly for each month and is easily configured to use your own feed format (an extension is provided for Google Calendar). It is visually customizable and exposes hooks for user-triggered events (like clicking or dragging an event).