draw.io - Online diagramming application
OpenToonz - OpenToonz is an animation program that is a free software version of Toonz, the animation software...
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.
Adobe Animate - Adobe Animate is a Flash, vector animation software.
PlantUML - PlantUML is an open-source tool that uses simple textual descriptions to draw UML diagrams.
Synfig Studio - Just another WordPress site