productboard - Beautiful and powerful product management.
draw.io - Online diagramming application
StoriesOnBoard - StoriesOnBoard helps agile teams build better products faster. The built-in guide helps you collect and prioritize ideas, understand user requirements, gather customer feedback, and validate feature ideas with internal & external stakeholders.
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.
Roadmap Space - Customer feedback & product management software for SaaS teams.
PlantUML - PlantUML is an open-source tool that uses simple textual descriptions to draw UML diagrams.