The Pencil Project: creating GUI diagrams and prototypes on the Firefox engine
The Pencil Project set as its goal the creation of a free (open source) medium for creating diagrams and GUI prototypes on the Firefox engine.
He was already discussed at Habrahabr the year before last ; Since then, export tools have appeared in Pencil (in HTML, PNG, Openoffice.org documents, Word and PDF), as well as clip art views.
Looks like that: ')
There are versions of the "Pencil", embedded in Firefox, and there are separate.
Pencil is distributed under the GPL v2 license and works wherever Firefox 3 is capable of working. For example, the first version of Pencil was tested on GNU / Linux 2.6 with GTK +, on Windows XP and Windows Vista.
Over there you can see several Mozilla bloggers in awe of the fact that in the Pencil in a couple of minutes you managed to jot down this interface: