960 Grid System is a CSS template that comes with corresponding Acorn, Fireworks, Flash, InDesign, GIMP, Inkscape, Illustrator, OmniGraffle, Photoshop, QuarkXPress, Visio, Exp Design, and printable templates to facilitate different stages of the web design process.
Graphviz is open source software for graph visualization, representing structural information as diagrams of abstract graphs and networks. The package includes web and interactive graphical interfaces, and auxiliary tools, libraries, and language bindings.
The HTML5 boilerplate is a base HTML/CSS/JS template for web design that offers cross-browser compatibility, cachine and compression rules, mobile browser optimizations, graceful degradation, and IE-specific classes. In addition to extensive documentation, there is an active Google Groups community for HTML5 boilerplate users.
Modest Maps is a display and interaction library for tile-based maps in Flash and Python that can display maps from external sources (e.g. OpenStreetMap, NASA Blue Marble, Yahoo!, Microsoft, but not Google Maps
Project Quincy allows users to trace the development of social networks and institutions over time and space using information about people, places and organizations. It is a Ruby on Rails application with a MySQL database that can be installed on a web server.