productboard - Beautiful and powerful product management.
draw.io - Online diagramming application
ProdPad - ProdPad helps your team gather ideas, surface the best ones and turn them into product specs, and then put it all on a product roadmap.
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.
ProductPlan - Cloud-based product roadmap software solution
PlantUML - PlantUML is an open-source tool that uses simple textual descriptions to draw UML diagrams.