integrated, web-based toolbox for creative work, both at school and in your free time. You use the toolbox along with various fully developed thematic universes: historical periods, fairy-tales, fantasy worlds, and current challenges, such as climate/environment. Use mind maps, cartoon creator, movie editor, or audio editor.
Storyboard That is a robust web tool that allows students to create and edit Storyboards. This site is simple to use and allows users to drag and drop stick figures and screen elements, as well as add their own content, to the storyboard time line. Enough tools and features to be really useful and not too many to confuse young users, this is a nice way for students to create storyboards for class projects, videos, or anything else you can think of including comic strips. There is a nice educator portal which has some lesson plans and example student work.
Not free, but free trial and reasonably priced for teachers
"Bring the world's best storyboard creator into your classroom!
From first grade to graduation, Storyboard That engages students with digital storytelling in the classroom."