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.
Mockuuups Studio - Fast and easy way to create product mockups on macOS, Windows and Linux.
draw.io - Online diagramming application
Mockup Generator - Create attractive product screenshots with just a few clicks
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.
Looped Live Mockups - Bring life into your project with unique live mockups