Cytoscape.js
A JavaScript graph library for analysis and visualisation (compatible with CommonJS/Node.js, AMD/Require.js, jQuery 1.4+, Bower, npm, and plain JavaScript)
Backgrid
Finally, an easily stylable semantic HTML data grid widget with a Javascript API that doesn't suck.
JS xls
Javascript XLS (Excel 97-2004 spreadsheet) parser and (one day) writer
Underscore.db
Pure JavaScript database based on Underscore for Node, node-webkit and the browser
JS Xlsx
Javascript XLSX / XLSM / XLSB (Excel 2007+) parser and (one day) writer
Knwl.js
A Natural Language Processor in JS
Tablecloth
A CSS and JS bootstrap to style and manipulate data tables
Crossfilter
Fast n-dimensional filtering and grouping of records.
Dc.js
Multi-Dimensional charting built to work natively with crossfilter rendered with d3.js
Oboe.js
A fresh approach to AJAX that speeds up web applications. Progressive JSON parser with an easy interface so you can use the objects before the http response completes.
Taffydb
TaffyDB - an open source JavaScript Database for your browser
jQuery treetable
jQuery plugin to show a tree structure in a table
JSON.js
JSON in JavaScript
Dimple
An object-oriented API for business analytics
Dgrid
A lightweight, mobile-ready, data-driven, modular grid widget designed for use with the Dojo object store
Datamaps
Maps for interactive data visualizations in Javascript
Loki JS
javascript embedded / in-memory database