Requstory - Requstory helps you write your user story quickly.
draw.io - Online diagramming application
Pine - A lightweight, modern macOS markdown editor written in Swift
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.
mockingbird - Mockingbird helps you you create and share clickable wireframes. Use it to make mockups of your website or application in minutes.
PlantUML - PlantUML is an open-source tool that uses simple textual descriptions to draw UML diagrams.