Storyboard That - Storyboard That is the world's best online storyboard creator.
draw.io - Online diagramming application
ToonDoo - ToonDoo is a fun and easy way to create comic strips without having to draw.
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.
Pixton - Our goal at Pixton Comics is to enable everyone in the world to make comics.
PlantUML - PlantUML is an open-source tool that uses simple textual descriptions to draw UML diagrams.