Linear - Streamlined issue tracking for software teams
draw.io - Online diagramming application
Distiller - Distiller's hosted continuous integration platform takes the pain out of mobile development through automated build, test, and deployment of your iOS apps.
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.
BugHerd - BugHerd: The Website Feedback Tool for Agencies
PlantUML - PlantUML is an open-source tool that uses simple textual descriptions to draw UML diagrams.