Time Visualization

• Timeliner– create timelines and timemaps using Google Spreadsheets (this tool is also available under the name TimeMapper – it is somewhat unclear as to the difference between Timeliner and TimeMapper)
• Timeline.js – an open-source tool that enables you to build visually-rich interactive timelines (hosted version)
• Timeline.js (JavaScript framework hosted on GitHub)
• SIMILE Timeline – Web Widget for Visualizing Temporal Data
• Recline.js – A simple but powerful library for building data applications in pure Javascript and HTML.
• Viewshare – a free platform for generating and customizing views (interactive maps, timelines, facets, tag clouds) that allow users to experience digital collections
• Timetoast – create timelines and share them on the web
• Timemap – Javascript library to help use online maps, including Google, OpenLayers, and Bing, with a SIMILE timeline. The library allows you to load one or more datasets in JSON, KML, or GeoRSS onto both a map and a timeline simultaneously.
• MyHistro – Hosted tool to create timelines (requires signup for a free account)

Geospatial Visualization

• GeoCommons – A public community and set of tools to access, visualize and analyze data with compelling map visualizations.
• Kartograph – A simple and lightweight framework for creating beautiful, interactive vector maps
• Leaflet – A lightweight JavaScript library for making tile-based interactive maps for desktop and mobile browsers.
• Mapbox – A web platform for hosting custom designed map tiles and a set of open source tools to produce them.
• Modest Maps – a small, extensible, and free library for designers and developers who want to use interactive maps in their own projects.
• OpenLayers – Javascript mapping library
• CartoDB – online tool for visualizing data on a map
• amMaps – JavaScript mapping library
• Viewshare – a free platform for generating and customizing views (interactive maps, timelines, facets, tag clouds) that allow users to experience digital collections
• Google Fusion Tables – A web application that makes it easy to host, manage, collaborate on, visualize, and publish data tables
• maps.stamen.com – map tiles and javascript library
• gmaps.js – a light-weight Google Maps API
• WorldMap – low barrier open source platform to explore, visualize, edit, collaborate with, and publish geospatial information.
• Ushahidi – online platform to collect and display information geospatially
• Timemap.js – Javascript library to help use online maps, including Google, OpenLayers, and Bing, with a SIMILE timeline. The library allows you to load one or more datasets in JSON, KML, or GeoRSS onto both a map and a timeline simultaneously.
• Storytelling with Maps – ESRI tool to build linear map-based narratives

Data Visualization

• NVD3 – Re-usable charts for d3.js
• Miso – open source toolkit designed to expedite the creation of high-quality interactive storytelling and data visualisation content.
• xCharts – a JavaScript library for building beautiful and custom data-driven chart visualizations for the web using D3.js
• Arbor.js – jQuery graph visualization library
• Cubism.js – a D3.js plugin for visualizing time series.
• D3.js – JavaScript based data visualization library
• Dance.js – A simple data-driven visualization framework based on Data.js and Underscore.js
• Envision.js – A Javascript library for creating fast, dynamic and interactive time series visualizations.
• Google Chart Tools – A collection of simple to use, customizable and free to use interactive charts and data tools.
• JavaScript InfoVis Toolkit – A Javascript library that provides tools for creating interactive data visualizations for the web.
• Peity – simple jQuery plugin that converts an element’s content into a simple mini pie, line or bar chart.
• Protovis – JavaScript library that composes custom views of data with simple marks such as bars and dots
• Rickshaw – library for creating interactive time series graphs based on D3.js.
• Sigma.js – Javascript library to display interactively static and dynamic graphs
• Flot – JQuery library for for line graphs and bar charts
• amCharts – JavaScript charting library
• Viewshare – a free platform for generating and customizing views (interactive maps, timelines, facets, tag clouds) that allow users to experience digital collections
• Google Fusion Tables – A web application that makes it easy to host, manage, collaborate on, visualize, and publish data tables
• Highcharts – charting library written in pure HTML5/JavaScript, offering intuitive, interactive charts to your web site or web application
• Tableau

Data Cleaning, Transformation, Management

• DataWrangler – interactive tool for data cleaning and transformation
• OpenRefine – desktop tool for cleaning and transforming data
• Miso Dataset – JavaScript client-side data transformation and management library. Dataset makes managing client-side data easy by handling loading, parsing, sorting, querying & manipulating data from all sorts of sources.
• Mr. Data Converter – web application that converts Excel data into one of several web-friendly formats, including HTML, JSON and XML
• Data Science Toolkit – Variety of data tools including street addresses to coordinates, file to text, coordinates to political areas, geographic names (countries, city, region) to coordinates, IP address to coordinates, HTML to text, text to people, etc.
• JSONView – a Firefox extension that helps you view JSON documents in the browser.
• JSON Editor – Tool for editing JSON strings
• JSON Online Editor
• dataset-tracking – plugin for the Mantis (http://www.mantisbt.org/) issue-tracker designed to support work-flows around “data publication” in research settings. The plugin enables editors to use Mantis’s issue-tracking features to coordinate work on cleaning datasets, aligning datasets to appropriate standards, and documenting datasets for publication.
• PANDA – Data library and data search engine
•  csvkit – a suite of powertools for working with Comma-separated values (CSV) files (command-line based)
• DataUp – An open source tool helping researchers document, manage, and archive their tabular data, DataUp operates within the scientist’s workflow and integrates with Microsoft® Excel.
• GeoJSONLint – site to validate and view your GeoJSON
• Named entity extraction extension for Open Refine
• Tabula – tool for extracting tabular data from a PDF
• Tabletop – takes a Google Spreadsheet and makes it easily accessible through JavaScript.

Design & Development Resources/Tools

• Bootswatch – tool for customizing color on a Bootstrap site
• Bootstrap Toolbox – Bootstrap Tools, Utilities, Generators and Templates
• Font Awesome: icon font designed to for use with Twitter Bootstrap
• Open Web Icons
• X-Ray Googles – browser tool to inspect and manipulate the code behind any web page
• Mozilla Thimble – tool to write and edit HTML and CSS right in your browser. Instantly preview your work. Then host and share your finished pages with a single click. 
• Sneakpeekit – free PDF sketch sheets and grid templates for various settings
• iconmonstr – free simple icons for your next project
• Typicons – all purpose, vector icons
• Bootsnip – growing library of free HTML snippets for Twitter Bootstrap
• Deployd – open source platform to design, build, and scale APIs for web and mobile apps
• Fuel UX – extends Twitter Bootstrap with additional lightweight JavaScript controls
• Entypo Pictogram Suite – a set of 250+ carefully crafted pictograms. The package contains an icon font — OpenType, TrueType and @font-face — EPS, PDF and PSD files. All released for free under the license CC BY-SA 3.0.
• Divshot – Bootstrap-based mockup interface builder for Web apps
• Gemicon – handcrafted icon set (600 icons in sizes 16, 32, 64px)
• Freebbble – resource of Dribbble freebies
• Ink – HTML/CSS Web design framework
• Bootstrap – HTML/CSS web design framework

Miscellaneous

• GeoNames – free DB with all countries and 8.000.000 placenames
• Natural Earth – public domain map dataset available at 1:10m, 1:50m, and 1:110 million scales.