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.
Synfig Studio - Just another WordPress site
draw.io - Online diagramming application
Blender - Blender is the open source, cross platform suite of tools for 3D creation.
yEd - yEd is a free desktop application to quickly create, import, edit, and automatically arrange diagrams. It runs on Windows, Mac OS X, and Unix/Linux.