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.
Webflow - Build dynamic, responsive websites in your browser. Launch with a click. Or export your squeaky-clean code to host wherever you'd like. Discover the professional website builder made for designers.
SmartDraw - Instead of starting with a blank screen, SmartDraw gives you the exact template you need.
Invision - Prototyping and collaboration for design teams
iRise - iRise combines fast prototyping with integrated requirements management to ensure you're managing the right requirements and user stories.
Zeplin - Collaboration app for UI designers & frontend developers