Rickshaw
JavaScript toolkit for creating interactive real-time graphs
Smoothie
Smoothie Charts: smooooooth JavaScript charts for realtime streaming data
D3 Cloud
Create word clouds in JavaScript.
Power Array
Boosted Performance Array
Heatmap.js
JavaScript Library for HTML5 canvas based heatmaps
Jszip
Create, read and edit .zip files with Javascript
Sheetrock
Quickly connect to, query, and lazy-load data from Google Spreadsheets.
Envision JS
Dynamic HTML5 visualization
Backgrid
Finally, an easily stylable semantic HTML data grid widget with a Javascript API that doesn't suck.
Holmes
Fast and easy searching inside a page
J Schema
A simple, easy to use data modeling framework for JavaScript
Aja.js
Ajax without XML : Asynchronous JavaScript and JavaScript/JSON(P)
Polychart2
Version 2 of Polychart.js
Socket.io
Realtime application framework for Node.JS, with HTML5 WebSockets and cross-browser fallbacks support.
Onionskin
A client- and server-side multi-layer cache manager library
jQuery File Upload
File Upload widget with multiple file selection, drag&drop support, progress bars and preview images for jQuery. Supports cross-domain, chunked and resumable file uploads and client-side image resizing. Works with any server-side platform (PHP, Python, Ruby on Rails, Java, Node.js, Go etc.) that supports standard HTML form file uploads.