FOSS Wireframing Tool!!!
I found the best open source wireframing tool, for the developers out there that sometimes like/have to pretend they are designers and need to create prototypes for graphical user interface, its called Pencil Project.
The Pencil Project runs as a standalone application or as a Firefox add-on. You can download it at the main site or directly from the evoluspencil code repository where you can also find more stencils packages.
Go get it now!