HolaBrief - A better way to create design briefs
Dia - Dia is a GTK+ based diagram creation program for GNU/Linux, MacOS X, Unix, and Windows, and is released under the GPL license.
Create Brief - Create a free shareable design brief. No email needed.
draw.io - Online diagramming application
GoodBrief - A random generator for design briefs.
yEd - yEd is a free desktop application to quickly create, import, edit, and automatically arrange diagrams. It runs on Windows, Mac OS X, and Unix/Linux.