What are some alternatives?
Cacoo - A cloud-based diagram maker for companies, teams, and you.
draw.io - Online diagramming application
SmartDraw - Instead of starting with a blank screen, SmartDraw gives you the exact template you need.
OmniGraffle - OmniGraffle is for creating precise graphics like website wireframes, an electrical system designs, or mapping out software class.
iRise - iRise combines fast prototyping with integrated requirements management to ensure you're managing the right requirements and user stories.
Gliffy - Gliffy is a powerful HTML5 online diagram maker. Create a flow chart, network diagram, UML diagram, organizational chart or wireframe with ease.