Vossier - Fortnightly UI design briefs, straight to your inbox.
draw.io - Online diagramming application
GoodBrief - A random generator for design briefs.
LucidChart - LucidChart is the missing link in online productivity suites. LucidChart allows users to create, collaborate on, and publish attractive flowcharts and other diagrams from a web browser.
Create Brief - Create a free shareable design brief. No email needed.
PlantUML - PlantUML is an open-source tool that uses simple textual descriptions to draw UML diagrams.