Pencil FireFox Add-on
Wouldn't it be nice if you could simply sketch out what you want your website to look and act like and then hand it over to the designer to let them work their magic? Prototyping tools let you do just that and the Pencil Firefox Add-on is one of the best
Pencil, which can be downloaded at the Firefox Add-on portal, is a free and opensource tool for making diagrams and GUI prototyping that everyone can use.
* Built-in stencils for diagraming and prototyping
* Multi-page document with background page
* On-screen text editing with rich-text supports
* PNG rasterizing
* Undo/redo supports
* Installing user-defined stencils
* Standard drawing operations: aligning, z-ordering, scaling, rotating...
* Adding external objects