The Pencil Project’s is built for the purpose of providing a free and open-source GUI prototyping tool that people can easily install and use to create mockups in popular desktop platforms. Pencil will always be free as it is released under the GPL version 2 and is available for virtually all platforms that Firefox 3 can run.
* Built-in stencils for diagraming and prototyping
* Multi-page document with background page
* Inter-page linkings!
* On-screen text editing with rich-text supports
* Exporting to HTML, PNG, Openoffice.org document, Word document and PDF.
* Undo/redo supports
* Installing user-defined stencils and templates
* Standard drawing operations: aligning, z-ordering, scaling, rotating…
* Adding external objects
* Personal Collection
* Clipart Browser
* Object snapping
* Sketchy Stencil
* And much more…
Highly recommended. But** I found out that keyboard cannot be resized!!! Solution see video demo
Pencil Project Demo – Free Mockup Tool
How to Install Collections in pencil
How to resize pencil collection