Invision - Prototyping and collaboration for design teams
SmartDraw - Instead of starting with a blank screen, SmartDraw gives you the exact template you need.
Proto.io - Create fully-interactive high-fidelity prototypes in minutes that look and work exactly like your app should. Sign up for a free 15-day trial and get started.
Creately - The new interface for work to ideate, plan, and execute
Zeplin - Collaboration app for UI designers & frontend developers
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.