"An easy to use, powerful, and flexible framework for building prototypes and production code on any kind of device."

Symbols of the controls for the Bootstrap library made by Twitter.

"LiveView is a specialized remote screen viewing application intended as a tool to help designers create graphics for mobile applications, it has also proven to be useful for creating quick and dirty simulations, demos, and experience prototypes"

"an online tool that makes it easy for you to create, link together, preview, and share mockups of your website or application."

"The Napkin Look & Feel is a pluggable Java look and feel that looks like it was scrawled on a napkin. You can use it to make provisional work actually look provisional, or just for fun."

Uhh... so it is just prototyping with HTML right? The tutorial never takes advantage of any XHTML-specific features.

" The Pencil Project's unique mission is to build a free and opensource tool for making diagrams and GUI prototyping that everyone can use." It is a Firefox 3 extension

"Polypage was designed to ease the process of showing multiple page states in html mock-ups. By adding simply adding class names to a document you can imply state and conditional view logic."

whoa. that's awesome. cheap as hell too if you think about it.

Recently updated wireframing stencil... in fact other than the ones shipping with OmniGraffle this may be the longest maintained OmniGraffle stencil out there.

another in a long list of screenshot annotation services.

"Like other Rosenfeld Media books, A Practitioner's Guide to Prototyping will take a hands-on approach, enabling you to develop prototypes with minimal muss and fuss. The book will discuss how prototypes are more than just a design tool by demonstrating h

"QEDWiki is a browser-based assembly canvas used to create simple mash-ups." Could be useful for prototyping?

Getting mixed reviews but I'd still like to thumb through it