Storyboarder - Storyboarder makes it easy to visualize a story as fast you can draw stick figures.
OpenToonz - OpenToonz is an animation program that is a free software version of Toonz, the animation software...
Storyboard Quick - Professional storyboards made in minutes: No drawing necessary!
Synfig Studio - Just another WordPress site
Boords - Making storyboards can be fiddly.
Blender - Blender is the open source, cross platform suite of tools for 3D creation.