Miro - Scalable, secure, cross-device and enterprise-ready team collaboration tool for distributed teams. Join 2M+ users & 8000+ teams from around the world.
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.
OpenBoard - The OpenBoard software is an interactive white board software.
draw.io - Online diagramming application
Conceptboard - Instant Whiteboards for Teams & Projects
PlantUML - PlantUML is an open-source tool that uses simple textual descriptions to draw UML diagrams.