draw.io - Online diagramming application
Steller - Everyone has a story to tell. Tell yours with photos, videos, and text.
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.
Requstory - Requstory helps you write your user story quickly.
PlantUML - PlantUML is an open-source tool that uses simple textual descriptions to draw UML diagrams.
Pine - A lightweight, modern macOS markdown editor written in Swift