Myths and Legends is a great tool that comes from England. This site is free and has a great storyboarding tool (see below).

You are provided with ready made characters, objects, speech bubbles, settings, sound effects and the ability to upload your own images to create your story. Students can manipulate objects to fit their story by flipping and resizing. Students can write up to ten chapters, too!

Begin by reading the Teacher Resource section. You will need to register your school to add classes. This will allow teachers to review and approve student work. Check out the other resources on the page for lesson ides.