What are some alternatives?
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.
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.
Cacoo - A cloud-based diagram maker for companies, teams, and you.
Moqups - The most stunning HTML5 app for creating resolution-independent SVG mockups, wireframes & interactive prototypes for your next project
SmartDraw - Instead of starting with a blank screen, SmartDraw gives you the exact template you need.
Balsamiq - Balsamiq. Rapid, effective and fun wireframing software.